diff --git a/init.lua b/init.lua
index a00cf9e..cbc684b 100644
--- a/init.lua
+++ b/init.lua
@@ -38,25 +38,40 @@ nether                = {}
 nether.modname        = minetest.get_current_modname()
 nether.path           = minetest.get_modpath(nether.modname)
 nether.get_translator = S
+                     -- nether.useBiomes allows other mods to know whether they can register ores etc. in the Nether.
+                     -- See mapgen.lua for an explanation of why minetest.read_schematic is being checked
+nether.useBiomes      = minetest.get_mapgen_setting("mg_name") ~= "v6" and minetest.read_schematic ~= nil
+
 
 -- Settings
-nether.DEPTH                      = -5000 -- The y location of the Nether
-nether.FASTTRAVEL_FACTOR          =     8 -- 10 could be better value for Minetest, since there's no sprint, but ex-Minecraft players will be mathing for 8
-nether.PORTAL_BOOK_LOOT_WEIGHTING =   0.9 -- Likelyhood of finding the Book of Portals (guide) in dungeon chests. Set to 0 to disable.
-nether.NETHER_REALM_ENABLED       =  true -- Setting to false disables the Nether and Nether portal
+nether.DEPTH_CEILING              =  -5000 -- The y location of the Nether's celing
+nether.DEPTH_FLOOR                = -11000 -- The y location of the Nether's floor
+nether.FASTTRAVEL_FACTOR          =      8 -- 10 could be better value for Minetest, since there's no sprint, but ex-Minecraft players will be mathing for 8
+nether.PORTAL_BOOK_LOOT_WEIGHTING =    0.9 -- Likelyhood of finding the Book of Portals (guide) in dungeon chests. Set to 0 to disable.
+nether.NETHER_REALM_ENABLED       =   true -- Setting to false disables the Nether and Nether portal
 
 
 -- Override default settings with values from the .conf file, if any are present.
 nether.FASTTRAVEL_FACTOR          = tonumber(minetest.settings:get("nether_fasttravel_factor") or nether.FASTTRAVEL_FACTOR)
 nether.PORTAL_BOOK_LOOT_WEIGHTING = tonumber(minetest.settings:get("nether_portalBook_loot_weighting") or nether.PORTAL_BOOK_LOOT_WEIGHTING)
 nether.NETHER_REALM_ENABLED       = minetest.settings:get_bool("nether_realm_enabled", nether.NETHER_REALM_ENABLED)
+nether.DEPTH_CEILING              = tonumber(minetest.settings:get("nether_depth_ymax") or nether.DEPTH_CEILING)
+nether.DEPTH_FLOOR                = tonumber(minetest.settings:get("nether_depth_ymin") or nether.DEPTH_FLOOR)
 
+if nether.DEPTH_FLOOR + 1000 > nether.DEPTH_CEILING then 
+	error("The lower limit of the Nether must be set at least 1000 lower than the upper limit, and more than 3000 is recommended. Set settingtypes.txt, or 'All Settings' -> 'Mods' -> 'nether' -> 'Nether depth'", 0)
+end
+nether.DEPTH = nether.DEPTH_CEILING -- Deprecated, use nether.DEPTH_CEILING instead.
 
 -- Load files
 dofile(nether.path .. "/portal_api.lua")
 dofile(nether.path .. "/nodes.lua")
 if nether.NETHER_REALM_ENABLED then
-	dofile(nether.path .. "/mapgen.lua")
+	if nether.useBiomes then
+		dofile(nether.path .. "/mapgen.lua")
+	else
+		dofile(nether.path .. "/mapgen_nobiomes.lua")
+	end
 end
 dofile(nether.path .. "/portal_examples.lua")
 
@@ -83,7 +98,7 @@ This opens to a truly hellish place, though for small mercies the air there is s
 The expedition parties have found no diamonds or gold, and after an experienced search party failed to return from the trail of a missing expedition party, I must conclude this is a dangerous place.]], 10 * nether.FASTTRAVEL_FACTOR),
 
 		is_within_realm = function(pos) -- return true if pos is inside the Nether
-			return pos.y < nether.DEPTH
+			return pos.y < nether.DEPTH_CEILING
 		end,
 
 		find_realm_anchorPos = function(surface_anchorPos)
@@ -91,7 +106,7 @@ The expedition parties have found no diamonds or gold, and after an experienced
 			local destination_pos = vector.divide(surface_anchorPos, nether.FASTTRAVEL_FACTOR)
 			destination_pos.x = math.floor(0.5 + destination_pos.x) -- round to int
 			destination_pos.z = math.floor(0.5 + destination_pos.z) -- round to int
-			destination_pos.y = nether.DEPTH - 1000 -- temp value so find_nearest_working_portal() returns nether portals
+			destination_pos.y = nether.DEPTH_CEILING - 1000 -- temp value so find_nearest_working_portal() returns nether portals
 
 			-- a y_factor of 0 makes the search ignore the altitude of the portals (as long as they are in the Nether)
 			local existing_portal_location, existing_portal_orientation =
@@ -100,7 +115,7 @@ The expedition parties have found no diamonds or gold, and after an experienced
 			if existing_portal_location ~= nil then
 				return existing_portal_location, existing_portal_orientation
 			else
-				local start_y = nether.DEPTH - math.random(500, 1500) -- Search starting altitude
+				local start_y = nether.DEPTH_CEILING - math.random(500, 1500) -- Search starting altitude
 				destination_pos.y = nether.find_nether_ground_y(destination_pos.x, destination_pos.z, start_y)
 				return destination_pos
 			end
diff --git a/mapgen.lua b/mapgen.lua
new file mode 100644
index 0000000..eaf2b71
--- /dev/null
+++ b/mapgen.lua
@@ -0,0 +1,500 @@
+--[[
+
+  Nether mod for minetest
+
+  Copyright (C) 2013 PilzAdam
+
+  Permission to use, copy, modify, and/or distribute this software for
+  any purpose with or without fee is hereby granted, provided that the
+  above copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR
+  BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
+  OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+  WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+  ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+  SOFTWARE.
+
+]]--
+
+
+-- Parameters
+
+local NETHER_CEILING = nether.DEPTH_CEILING
+local NETHER_FLOOR   = nether.DEPTH_FLOOR
+local TCAVE = 0.6
+local BLEND = 128
+
+
+-- Stuff
+
+local math_max, math_min = math.max, math.min -- avoid needing table lookups each time a common math function is invoked
+
+if minetest.read_schematic == nil then
+	-- Using biomes to create the Nether requires the ability for biomes to set "node_cave_liquid = air".
+	-- This feature was introduced by paramat in b1b40fef1 on 2019-05-19, but we can't test for
+	-- it directly. However b2065756c was merged a few months later (in 2019-08-14) and it is easy
+	-- to directly test for - it adds minetest.read_schematic() - so we use this as a proxy-test
+	-- for whether the Minetest engine is recent enough to have implemented node_cave_liquid=air
+	error("This " .. nether.modname .. " mapgen requires Minetest v5.1 or greater, use mapgen_nobiomes.lua instead.", 0)
+end
+
+local function override_underground_biomes()
+	-- https://forum.minetest.net/viewtopic.php?p=257522#p257522
+	-- Q: Is there a way to override an already-registered biome so I can get it out of the
+	--    way of my own underground biomes without disturbing the other biomes registered by
+	--    default?
+	-- A: No, all you can do is use a mod to clear all biomes then re-register the complete
+	--    set but with your changes. It has been described as hacky but this is actually the
+	--    official way to alter biomes, most mods and subgames would want to completely change
+	--    all biomes anyway.
+	--    To avoid the engine side of mapgen becoming overcomplex the approach is to require mods
+	--    to do slightly more complex stuff in Lua.
+
+	-- take a copy of all biomes, decorations, and ores. Regregistering a biome changes its ID, so
+	-- any decorations or ores using the 'biomes' field must afterwards be cleared and re-registered.
+	-- https://github.com/minetest/minetest/issues/9288
+	local registered_biomes_copy      = {}
+	local registered_decorations_copy = {}
+	local registered_ores_copy        = {}
+
+	for old_biome_key, old_biome_def in pairs(minetest.registered_biomes) do
+	   registered_biomes_copy[old_biome_key] = old_biome_def
+	end
+	for old_decoration_key, old_decoration_def in pairs(minetest.registered_decorations) do
+	   registered_decorations_copy[old_decoration_key] = old_decoration_def
+	end
+	for old_ore_key, old_ore_def in pairs(minetest.registered_ores) do
+		registered_ores_copy[old_ore_key] = old_ore_def
+	 end
+
+	-- clear biomes, decorations, and ores
+	minetest.clear_registered_decorations()
+	minetest.clear_registered_ores()
+	minetest.clear_registered_biomes()
+
+	-- Restore biomes, adjusted to not overlap the Nether
+	for biome_key, new_biome_def in pairs(registered_biomes_copy) do
+		local biome_y_max, biome_y_min = tonumber(new_biome_def.y_max), tonumber(new_biome_def.y_min)
+
+		if biome_y_max > NETHER_FLOOR and biome_y_min < NETHER_CEILING then
+			-- This biome occupies some or all of the depth of the Nether, shift/crop it.
+			local spaceOccupiedAbove = biome_y_max - NETHER_CEILING
+			local spaceOccupiedBelow = NETHER_FLOOR - biome_y_min
+			if spaceOccupiedAbove >= spaceOccupiedBelow or biome_y_min <= -30000 then
+				-- place the biome above the Nether
+				-- We also shift biomes which extend to the bottom of the map above the Nether, since they
+				-- likely only extend that deep as a catch-all, and probably have a role nearer the surface.
+				new_biome_def.y_min = NETHER_CEILING + 1
+				new_biome_def.y_max = math_max(biome_y_max, NETHER_CEILING + 2)
+			else
+				-- shift the biome to below the Nether
+				new_biome_def.y_max = NETHER_FLOOR - 1
+				new_biome_def.y_min = math_min(biome_y_min, NETHER_CEILING - 2)
+			end
+		end
+		minetest.register_biome(new_biome_def)
+	end
+
+	-- Restore biome decorations
+	for decoration_key, new_decoration_def in pairs(registered_decorations_copy) do
+	   minetest.register_decoration(new_decoration_def)
+	end
+	-- Restore biome ores
+	for ore_key, new_ore_def in pairs(registered_ores_copy) do
+		minetest.register_ore(new_ore_def)
+	 end
+ end
+
+-- Shift any overlapping biomes out of the way before we create the Nether biomes
+override_underground_biomes()
+
+-- nether:native_mapgen is used to prevent ores and decorations being generated according
+-- to landforms created by the native mapgen.
+-- Ores and decorations are registered against "nether:rack" instead, and the lua
+-- on_generate() callback will carve the Nether with nether:rack before invoking
+-- generate_decorations and generate_ores.
+minetest.register_node("nether:native_mapgen", {})
+
+minetest.register_biome({
+	name = "nether_caverns",
+	node_stone  = "nether:native_mapgen", -- nether:native_mapgen is used here to prevent the native mapgen from placing ores and decorations.
+	node_filler = "nether:native_mapgen", -- The lua on_generate will transform nether:rack_native into nether:rack then decorate and add ores.
+	node_dungeon = "nether:brick",
+	--node_dungeon_alt = "default:mossycobble",
+	node_dungeon_stair = "stairs:stair_nether_brick",
+	-- Setting node_cave_liquid to "air" avoids the need to filter lava and water out of the mapchunk and
+	-- surrounding shell (overdraw nodes beyond the mapchunk).
+	-- This feature was introduced by paramat in b1b40fef1 on 2019-05-19, and this mapgen.lua file should only
+	-- be run if the Minetest version includes it. The earliest tag made after 2019-05-19 is 5.1.0 on 2019-10-13,
+	-- however we shouldn't test version numbers. minetest.read_schematic() was added by b2065756c and merged in
+	-- 2019-08-14 and is easy to test for, we don't use it but it should make a good proxy-test for whether the
+	-- Minetest version is recent enough to have implemented node_cave_liquid=air
+	node_cave_liquid = "air",
+	y_max = NETHER_CEILING,
+	y_min = NETHER_FLOOR,
+	vertical_blend = 0,
+	heat_point = 50,
+	humidity_point = 50,
+})
+
+
+-- Ores and decorations
+
+dofile(nether.path .. "/mapgen_decorations.lua")
+
+minetest.register_ore({
+	ore_type       = "scatter",
+	ore            = "nether:glowstone",
+	wherein        = "nether:rack",
+	clust_scarcity = 11 * 11 * 11,
+	clust_num_ores = 3,
+	clust_size     = 2,
+	y_max = NETHER_CEILING,
+	y_min = NETHER_FLOOR,
+})
+
+minetest.register_ore({
+	ore_type       = "scatter",
+	ore            = "default:lava_source",
+	wherein        = "nether:rack",
+	clust_scarcity = 32 * 32 * 32,
+	clust_num_ores = 4,
+	clust_size     = 2,
+	y_max = NETHER_CEILING,
+	y_min = NETHER_FLOOR,
+})
+
+minetest.register_ore({
+	ore_type        = "blob",
+	ore             = "nether:sand",
+	wherein         = "nether:rack",
+	clust_scarcity  = 14 * 14 * 14,
+	clust_size      = 8,
+	y_max = NETHER_CEILING,
+	y_min = NETHER_FLOOR
+})
+
+
+-- Mapgen
+
+-- 3D noise
+
+local np_cave = {
+	offset = 0,
+	scale = 1,
+	spread = {x = 384, y = 128, z = 384}, -- squashed 3:1
+	seed = 59033,
+	octaves = 5,
+	persist = 0.7,
+	lacunarity = 2.0,
+	--flags = ""
+}
+
+-- Buffers and objects we shouldn't recreate every on_generate
+
+local nobj_cave = nil
+local nbuf_cave = nil
+local dbuf = nil
+
+local yblmin = NETHER_FLOOR   + BLEND * 2
+local yblmax = NETHER_CEILING - BLEND * 2
+
+-- Content ids
+
+local c_air              = minetest.get_content_id("air")
+local c_netherrack       = minetest.get_content_id("nether:rack")
+local c_netherbrick      = minetest.get_content_id("nether:brick")
+local c_netherbrick_slab = minetest.get_content_id("stairs:slab_nether_brick")
+local c_netherfence      = minetest.get_content_id("nether:fence_nether_brick")
+local c_glowstone        = minetest.get_content_id("nether:glowstone")
+local c_lava_source      = minetest.get_content_id("default:lava_source")
+local c_native_mapgen    = minetest.get_content_id("nether:native_mapgen")
+
+
+-- Dungeon excavation functions
+
+function build_dungeon_room_list(data, area)
+
+	local result = {}
+
+	-- Unfortunately gennotify only returns dungeon rooms, not corridors.
+	-- We don't need to check for temples because only dungeons are generated in biomes
+	-- that define their own dungeon nodes.
+	local gennotify = minetest.get_mapgen_object("gennotify")
+	local roomLocations = gennotify["dungeon"] or {}
+
+	-- Excavation should still know to stop if a cave or corridor has removed the dungeon wall.
+	-- See MapgenBasic::generateDungeons in mapgen.cpp for max room sizes.
+	local maxRoomSize = 18
+	local maxRoomRadius = math.ceil(maxRoomSize / 2)
+
+	local xStride, yStride, zStride = 1, area.ystride, area.zstride
+	local minEdge, maxEdge = area.MinEdge, area.MaxEdge
+
+	for _, roomPos in ipairs(roomLocations) do
+
+		if area:containsp(roomPos) then -- this safety check does not appear to be necessary, but lets make it explicit
+
+			local room_vi = area:indexp(roomPos)
+			--data[room_vi] = minetest.get_content_id("default:torch") -- debug
+
+			local startPos = vector.new(roomPos)
+			if roomPos.y + 1 <= maxEdge.y and data[room_vi + yStride] == c_air then
+				-- The roomPos coords given by gennotify are at floor level, but whenever possible we
+				-- want to be performing searches a node higher than floor level to avoids dungeon chests.
+				startPos.y = startPos.y + 1
+				room_vi = area:indexp(startPos)
+			end
+
+			local bound_min_x = math_max(minEdge.x, roomPos.x - maxRoomRadius)
+			local bound_min_y = math_max(minEdge.y, roomPos.y - 1) -- room coords given by gennotify are on the floor
+			local bound_min_z = math_max(minEdge.z, roomPos.z - maxRoomRadius)
+
+			local bound_max_x = math_min(maxEdge.x, roomPos.x + maxRoomRadius)
+			local bound_max_y = math_min(maxEdge.y, roomPos.y + maxRoomSize) -- room coords given by gennotify are on the floor
+			local bound_max_z = math_min(maxEdge.z, roomPos.z + maxRoomRadius)
+
+			local room_min = vector.new(startPos)
+			local room_max = vector.new(startPos)
+
+			local vi = room_vi
+			while room_max.y < bound_max_y and data[vi + yStride] == c_air do
+				room_max.y = room_max.y + 1
+				vi = vi + yStride
+			end
+
+			vi = room_vi
+			while room_min.y > bound_min_y and data[vi - yStride] == c_air do
+				room_min.y = room_min.y - 1
+				vi = vi - yStride
+			end
+
+			vi = room_vi
+			while room_max.z < bound_max_z and data[vi + zStride] == c_air do
+				room_max.z = room_max.z + 1
+				vi = vi + zStride
+			end
+
+			vi = room_vi
+			while room_min.z > bound_min_z and data[vi - zStride] == c_air do
+				room_min.z = room_min.z - 1
+				vi = vi - zStride
+			end
+
+			vi = room_vi
+			while room_max.x < bound_max_x and data[vi + xStride] == c_air do
+				room_max.x = room_max.x + 1
+				vi = vi + xStride
+			end
+
+			vi = room_vi
+			while room_min.x > bound_min_x and data[vi - xStride] == c_air do
+				room_min.x = room_min.x - 1
+				vi = vi - xStride
+			end
+
+			local roomInfo = vector.new(roomPos)
+			roomInfo.minp = room_min
+			roomInfo.maxp = room_max
+			result[#result + 1] = roomInfo
+		end
+	end
+
+	return result;
+end
+
+-- Only partially excavates dungeons, the rest is left as an exercise for the player ;)
+-- (Corridors and the parts of rooms which extend beyond the emerge boundary will remain filled)
+function excavate_dungeons(data, area, rooms)
+
+	-- any air from the native mapgen has been replaced by netherrack, but
+	-- we don't want this inside dungeons, so fill dungeon rooms with air
+	for _, roomInfo in ipairs(rooms) do
+
+		local room_min = roomInfo.minp
+		local room_max = roomInfo.maxp
+
+		for z = room_min.z, room_max.z do
+			for y = room_min.y, room_max.y do
+				local vi = area:index(room_min.x, y, z)
+				for x = room_min.x, room_max.x do
+					if data[vi] == c_netherrack then data[vi] = c_air end
+					vi = vi + 1
+				end
+			end
+		end
+	end
+end
+
+-- Since we already know where all the rooms and their walls are, and have all the nodes stored
+-- in a voxelmanip already, we may as well add a little Nether flair to the dungeons found here.
+function decorate_dungeons(data, area, rooms)
+
+	local xStride, yStride, zStride = 1, area.ystride, area.zstride
+	local minEdge, maxEdge = area.MinEdge, area.MaxEdge
+
+	for _, roomInfo in ipairs(rooms) do
+
+		local room_min, room_max = roomInfo.minp, roomInfo.maxp
+		local room_size = vector.distance(room_min, room_max)
+
+		if room_size > 10 then
+			local room_seed = roomInfo.x + 3 * roomInfo.z + 13 * roomInfo.y
+			local window_y  = roomInfo.y + math_min(2, room_max.y - roomInfo.y - 1)
+
+			if room_seed % 3 == 0 and room_max.y < maxEdge.y then
+				-- Glowstone chandelier
+				local vi = area:index(roomInfo.x, room_max.y + 1, roomInfo.z)
+				if data[vi] == c_netherbrick then data[vi] = c_glowstone end
+
+			elseif room_seed % 4 == 0 and room_min.y > minEdge.y
+				   and room_min.x > minEdge.x and room_max.x < maxEdge.x
+				   and room_min.z > minEdge.z and room_max.z < maxEdge.z then
+				-- lava well (feel free to replace with a fancy schematic)
+				local vi = area:index(roomInfo.x, room_min.y, roomInfo.z)
+				if data[vi - yStride] == c_netherbrick then data[vi - yStride] = c_lava_source end
+				if data[vi - zStride] == c_air then data[vi - zStride] = c_netherbrick_slab end
+				if data[vi + zStride] == c_air then data[vi + zStride] = c_netherbrick_slab end
+				if data[vi - xStride] == c_air then data[vi - xStride] = c_netherbrick_slab end
+				if data[vi + xStride] == c_air then data[vi + xStride] = c_netherbrick_slab end
+			end
+
+			-- Barred windows
+			if room_seed % 7 < 5 and room_max.x - room_min.x >= 4 and room_max.z - room_min.z >= 4
+			   and window_y >= minEdge.y and window_y + 1 <= maxEdge.y
+			   and room_min.x > minEdge.x and room_max.x < maxEdge.x
+			   and room_min.z > minEdge.z and room_max.z < maxEdge.z then
+				--data[area:indexp(roomInfo)] = minetest.get_content_id("default:mese_post_light") -- debug
+
+				-- Until whisper glass is added, every window will be made of netherbrick fence (rather
+				-- than material depending on room_seed)
+				local window_node = c_netherfence
+
+				local vi_min = area:index(room_min.x - 1, window_y, roomInfo.z)
+				local vi_max = area:index(room_max.x + 1, window_y, roomInfo.z)
+				local locations = {-zStride, zStride, -zStride + yStride, zStride + yStride}
+				for _, offset in ipairs(locations) do
+					if data[vi_min + offset] == c_netherbrick then data[vi_min + offset] = window_node end
+					if data[vi_max + offset] == c_netherbrick then data[vi_max + offset] = window_node end
+				end
+				vi_min = area:index(roomInfo.x, window_y, room_min.z - 1)
+				vi_max = area:index(roomInfo.x, window_y, room_max.z + 1)
+				locations = {-xStride, xStride, -xStride + yStride, xStride + yStride}
+				for _, offset in ipairs(locations) do
+					if data[vi_min + offset] == c_netherbrick then data[vi_min + offset] = window_node end
+					if data[vi_max + offset] == c_netherbrick then data[vi_max + offset] = window_node end
+				end
+			end
+
+			-- Weeds on the floor once Nether weeds are added
+		end
+	end
+end
+
+
+-- On-generated function
+
+local function on_generated(minp, maxp, seed)
+
+	if minp.y > NETHER_CEILING or maxp.y < NETHER_FLOOR then
+		return
+	end
+
+	local vm, emerge_min, emerge_max = minetest.get_mapgen_object("voxelmanip")
+	local area = VoxelArea:new{MinEdge=emerge_min, MaxEdge=emerge_max}
+	local data = vm:get_data(dbuf)
+
+	local x0, y0, z0 = minp.x, math_max(minp.y, NETHER_FLOOR),   minp.z
+	local x1, y1, z1 = maxp.x, math_min(maxp.y, NETHER_CEILING), maxp.z
+
+	local yCaveStride = x1 - x0 + 1
+	local zCaveStride = yCaveStride * yCaveStride
+	local chulens = {x = yCaveStride, y = yCaveStride, z = yCaveStride}
+
+	nobj_cave = nobj_cave or minetest.get_perlin_map(np_cave, chulens)
+	local nvals_cave = nobj_cave:get3dMap_flat(minp, nbuf_cave)
+
+
+	local dungeonRooms = build_dungeon_room_list(data, area)
+
+	for y = y0, y1 do -- Y loop first to minimise tcave calculations
+
+		local tcave = TCAVE
+		if y > yblmax then tcave = TCAVE + ((y - yblmax) / BLEND) ^ 2 end
+		if y < yblmin then tcave = TCAVE + ((yblmin - y) / BLEND) ^ 2 end
+
+		for z = z0, z1 do
+			local vi = area:index(x0, y, z) -- Initial voxelmanip index
+			local ni = (z - z0) * zCaveStride + (y - y0) * yCaveStride + 1
+
+			for x = x0, x1 do
+
+				local id = data[vi] -- Existing node
+
+				if nvals_cave[ni] > tcave then
+					data[vi] = c_air
+				elseif id == c_air or id == c_native_mapgen then
+					data[vi] = c_netherrack -- excavate_dungeons() will mostly reverse this inside dungeons
+				end
+
+				ni = ni + 1
+				vi = vi + 1
+			end
+		end
+	end
+
+	-- any air from the native mapgen has been replaced by netherrack, but we
+	-- don't want netherrack inside dungeons, so fill known dungeon rooms with air.
+	excavate_dungeons(data, area, dungeonRooms)
+	decorate_dungeons(data, area, dungeonRooms)
+
+	vm:set_data(data)
+
+	-- avoid generating decorations on the underside of the bottom of the nether
+	if minp.y > NETHER_FLOOR and maxp.y < NETHER_CEILING then minetest.generate_decorations(vm) end
+
+	minetest.generate_ores(vm)
+	vm:set_lighting({day = 0, night = 0}, minp, maxp)
+	vm:calc_lighting()
+	vm:update_liquids()
+	vm:write_to_map()
+end
+
+
+-- use knowledge of the nether mapgen algorithm to return a suitable ground level for placing a portal.
+function nether.find_nether_ground_y(target_x, target_z, start_y)
+	local nobj_cave_point = minetest.get_perlin(np_cave)
+	local air = 0 -- Consecutive air nodes found
+
+	for y = start_y, math_max(NETHER_FLOOR + BLEND, start_y - 4096), -1 do
+		local nval_cave = nobj_cave_point:get3d({x = target_x, y = y, z = target_z})
+
+		if nval_cave > TCAVE then -- Cavern
+			air = air + 1
+		else -- Not cavern, check if 4 nodes of space above
+			if air >= 4 then
+				-- Check volume for non-natural nodes
+				local minp = {x = target_x - 1, y = y    , z = target_z - 2}
+				local maxp = {x = target_x + 2, y = y + 4, z = target_z + 2}
+				if nether.volume_is_natural(minp, maxp) then
+					return y + 1
+				else -- Restart search a little lower
+					nether.find_nether_ground_y(target_x, target_z, y - 16)
+				end
+			else -- Not enough space, reset air to zero
+				air = 0
+			end
+		end
+	end
+
+	return math_max(start_y, NETHER_FLOOR + BLEND) -- Fallback
+end
+
+-- We don't need to be gen-notified of temples because only dungeons will be generated
+-- if a biome defines the dungeon nodes
+minetest.set_gen_notify({dungeon = true})
+
+minetest.register_on_generated(on_generated)
\ No newline at end of file
diff --git a/mapgen_decorations.lua b/mapgen_decorations.lua
new file mode 100644
index 0000000..b210db8
--- /dev/null
+++ b/mapgen_decorations.lua
@@ -0,0 +1,138 @@
+--[[
+
+  Register decorations for Nether mapgen
+
+  Copyright (C) 2020 Treer
+
+  Permission to use, copy, modify, and/or distribute this software for
+  any purpose with or without fee is hereby granted, provided that the
+  above copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR
+  BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
+  OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+  WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+  ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+  SOFTWARE.
+
+]]--
+
+-- Lava is unreliable in the old Nether mapgen because it removes lava
+-- from the overdraw areas, so any decorations involving lava will often
+-- have the lava missing depending on whether nearby chunks were already
+-- emerged or not before the decoration was placed.
+local allow_lava_decorations = nether.useBiomes
+
+local _ = {name = "air",                     prob = 0}
+local A = {name = "air",                     prob = 255, force_place = true}
+local G = {name = "nether:glowstone",        prob = 255, force_place = true}
+local N = {name = "nether:rack",             prob = 255}
+local S = {name = "nether:sand",             prob = 255, force_place = true}
+local L = {name = "default:lava_source",     prob = 255, force_place = true}
+
+
+-- =================
+--    Stalactites
+-- =================
+
+local schematic_GlowstoneStalactite = {
+    size = {x = 5, y = 10, z = 5},
+    data = {
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, N, G, N, _,
+        _, N, N, N, _,
+
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, G, _, _,
+        _, _, G, _, _,
+        _, G, G, G, _,
+        N, G, G, G, N,
+        N, N, G, N, N,
+
+        _, _, N, _, _,   -- ypos 0, prob 25% (64/256)
+        _, _, G, _, _,   -- ypos 1, prob 37% (96/256)
+        _, _, G, _, _,   -- ypos 2, prob 100%
+        _, _, G, _, _,   -- ypos 3, prob 100%
+        _, _, G, G, _,   -- ypos 4, prob 50% (128/256) to make half of stalactites asymmetric
+        _, G, G, G, _,   -- ypos 5, prob 75% (192/256)
+        _, G, G, G, _,   -- ypos 6, prob 75% (192/256)
+        _, G, G, G, _,   -- ypos 7, prob 100%
+        G, G, G, G, G,   -- ypos 8, prob 100%
+        N, G, G, G, N,   -- ypos 9, prob 75% (192/256)
+
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, G, _, _,
+        _, _, G, _, _,
+        _, _, G, _, _,
+        _, G, G, G, _,
+        N, G, G, G, N,
+        N, N, G, N, N,
+
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, _, _, _, _,
+        _, N, G, N, _,
+        _, N, N, N, _
+    },
+    -- Y-slice probabilities do not function correctly for ceiling schematic
+    -- decorations because they are inverted, so ypos numbers have been inverted
+    -- to match, and a larger offset in place_offset_y should be used (e.g. -3).
+    yslice_prob = {
+        {ypos = 9, prob = 192},
+        {ypos = 6, prob = 192},
+        {ypos = 5, prob = 192},
+        {ypos = 4, prob = 128},
+        {ypos = 1, prob = 96},
+        {ypos = 0, prob = 64}
+    }
+}
+
+minetest.register_decoration({
+    name = "Glowstone stalactite",
+    deco_type = "schematic",
+    place_on = "nether:rack",
+    sidelen = 80,
+    fill_ratio = 0.0004,
+    biomes = {"nether_caverns"},
+    y_max = nether.DEPTH_CEILING, -- keep compatibility with mapgen_nobiomes.lua
+    y_min = nether.DEPTH_FLOOR,
+    schematic = schematic_GlowstoneStalactite,
+    flags = "place_center_x,place_center_z,force_placement,all_ceilings",
+    place_offset_y=-3
+})
+
+minetest.register_decoration({
+    name = "Netherrack stalactite",
+    deco_type = "schematic",
+    place_on = "nether:rack",
+    sidelen = 80,
+    fill_ratio = 0.0007,
+    biomes = {"nether_caverns"},
+    y_max = nether.DEPTH_CEILING, -- keep compatibility with mapgen_nobiomes.lua
+    y_min = nether.DEPTH_FLOOR,
+    schematic = schematic_GlowstoneStalactite,
+    replacements = {["nether:glowstone"] = "nether:rack"},
+    flags = "place_center_x,place_center_z,all_ceilings",
+    place_offset_y=-3
+})
diff --git a/mapgen_nobiomes.lua b/mapgen_nobiomes.lua
index 6359804..fb707e5 100644
--- a/mapgen_nobiomes.lua
+++ b/mapgen_nobiomes.lua
@@ -19,11 +19,11 @@
 
 ]]--
 
-nether.DEPTH_FLOOR = -30912 -- this mapgen will create Nether all the way down
 
 -- Parameters
 
-local NETHER_DEPTH = nether.DEPTH
+local NETHER_CEILING = nether.DEPTH_CEILING
+local NETHER_FLOOR   = nether.DEPTH_FLOOR
 local TCAVE = 0.6
 local BLEND = 128
 
@@ -44,13 +44,15 @@ local np_cave = {
 
 -- Stuff
 
-local yblmax = NETHER_DEPTH - BLEND * 2
-
+local yblmin = NETHER_FLOOR   + BLEND * 2
+local yblmax = NETHER_CEILING - BLEND * 2
 
 
 
 -- Mapgen
 
+dofile(nether.path .. "/mapgen_decorations.lua")
+
 -- Initialize noise object, localise noise and data buffers
 
 local nobj_cave = nil
@@ -92,15 +94,15 @@ local c_netherrack = minetest.get_content_id("nether:rack")
 -- On-generated function
 
 minetest.register_on_generated(function(minp, maxp, seed)
-	if minp.y > NETHER_DEPTH then
+	if minp.y > NETHER_CEILING or maxp.y < NETHER_FLOOR then
 		return
 	end
 
 	local x1 = maxp.x
-	local y1 = maxp.y
+	local y1 = math.min(maxp.y, NETHER_CEILING)
 	local z1 = maxp.z
 	local x0 = minp.x
-	local y0 = minp.y
+	local y0 = math.max(minp.y, NETHER_FLOOR)
 	local z0 = minp.z
 
 	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
@@ -126,11 +128,9 @@ minetest.register_on_generated(function(minp, maxp, seed)
 		local tcave
 		local in_chunk_y = false
 		if y >= y0 and y <= y1 then
-			if y > yblmax then
-				tcave = TCAVE + ((y - yblmax) / BLEND) ^ 2
-			else
-				tcave = TCAVE
-			end
+			tcave = TCAVE
+			if y > yblmax then tcave = TCAVE + ((y - yblmax) / BLEND) ^ 2 end
+			if y < yblmin then tcave = TCAVE + ((yblmin - y) / BLEND) ^ 2 end
 			in_chunk_y = true
 		end
 
@@ -189,6 +189,10 @@ minetest.register_on_generated(function(minp, maxp, seed)
 	end
 
 	vm:set_data(data)
+
+	-- avoid generating decorations on the underside of the bottom of the nether
+	if minp.y > NETHER_FLOOR and maxp.y < NETHER_CEILING then minetest.generate_decorations(vm) end
+
 	vm:set_lighting({day = 0, night = 0}, minp, maxp)
 	vm:calc_lighting()
 	vm:update_liquids()
diff --git a/settingtypes.txt b/settingtypes.txt
index dbea779..fca72e5 100644
--- a/settingtypes.txt
+++ b/settingtypes.txt
@@ -16,4 +16,10 @@ nether_realm_enabled (Enable Nether realm & portal) bool true
 nether_enable_portal_example_floatlands (Enable example portal: Floatlands) bool false
 
 # Enables the Surface-travel portal api code example
-nether_enable_portal_example_surfacetravel (Enable example portal: Surface-travel) bool false
\ No newline at end of file
+nether_enable_portal_example_surfacetravel (Enable example portal: Surface-travel) bool false
+
+[Nether depth]
+#The depth where the Nether begins / the Nether ceiling
+nether_depth_ymax (Upper limit of Nether) int -5000 -30000 32767
+#The lower limit of the Nether must be at least 1000 lower than the upper limit, and more than 3000 lower is recommended.
+nether_depth_ymin (Lower limit of Nether) int -11000 -32768 30000
\ No newline at end of file