diff --git a/bubble_caves/init.lua b/bubble_caves/init.lua
new file mode 100644
index 0000000..c7d609d
--- /dev/null
+++ b/bubble_caves/init.lua
@@ -0,0 +1,144 @@
+local modpath = minetest.get_modpath(minetest.get_current_modname())
+local mapgen_test_path = minetest.get_modpath("mapgen_test")
+--local S = minetest.get_translator(minetest.get_current_modname())
+local c_air = minetest.get_content_id("air")
+
+local c_glow
+if minetest.get_modpath("df_underworld_items") then
+	c_glow = minetest.get_content_id("df_underworld_items:glowstone")
+end
+
+local perlin_params = {
+	offset = 0,
+	scale = 1,
+	spread = {x=1000, y=500, z=1000},
+	seed = 501221,
+	octaves = 3,
+	persist = 0.67
+}
+local data = {}
+local light_data = {}
+local light = 15 + (15 * 16)
+
+local max_depth = -5000
+local min_depth = -6000
+
+local noise_obj
+
+local block_size = 80
+local cube_inside = 1/math.sqrt(3) -- https://www.quora.com/What-is-the-largest-volume-of-a-cube-that-can-be-enclosed-in-a-sphere-of-diameter-2
+
+local get_bubbles = function(pos)
+	noise_obj = noise_obj or minetest.get_perlin(perlin_params)
+	local bubbles = {}
+	local next_seed = math.random(1000000)
+	for block_x = -1, 1 do
+		for block_y = -1, 1 do
+			for block_z = -1, 1 do
+				local this_pos = vector.add(pos, {x=block_x*block_size, y=block_y*block_size, z=block_z*block_size})
+				math.randomseed(this_pos.x + this_pos.y*8 + this_pos.z*16)
+				this_pos.x = this_pos.x + math.floor(math.random()*block_size - block_size/2)
+				this_pos.y = this_pos.y + math.floor(math.random()*block_size - block_size/2)
+				this_pos.z = this_pos.z + math.floor(math.random()*block_size - block_size/2)
+				local noise_val = math.min(noise_obj:get_3d(this_pos), 1.0)
+				if noise_val > 0 then
+					local radius = noise_val*block_size*math.random()+5
+					local y = this_pos.y
+					if y + radius < max_depth  and y - radius > min_depth then -- make sure bubbles remain within the layer
+						if mapgen_test_path then
+							if noise_val < 0.1 then
+								mapgen_test.record_first_location("bubble cave sparse", this_pos, "a bubble cave in a sparsely populated region")
+							elseif noise_val < 0.55 and noise_val > 0.45 then
+								mapgen_test.record_first_location("bubble cave middle", this_pos, "a bubble cave in a middlingly populated region")
+							elseif noise_val > 0.9 then
+								mapgen_test.record_first_location("bubble cave dense", this_pos, "a bubble cave in a densely populated region")
+							end
+						end
+						table.insert(bubbles, {loc=this_pos, radius=radius})
+					end
+				end
+			end
+		end
+	end
+	math.randomseed(next_seed)
+	return bubbles
+end
+
+
+if mapgen_test_path then
+	mapgen_test.log_time_settings("bubble_caves")
+end
+
+minetest.register_on_generated(function(minp, maxp, seed)
+	if minp.y > max_depth or maxp.y < min_depth then
+		return
+	end
+
+	local nearby_bubbles = get_bubbles({x=minp.x+block_size/2, y=minp.y+block_size/2, z=minp.z+block_size/2})
+	if not next(nearby_bubbles) then
+		return
+	end
+
+	if mapgen_test_path then
+		mapgen_test.log_time_start("bubble_caves")
+	end
+	
+	local vm, emin, emax = minetest.get_mapgen_object("voxelmanip")
+	local area = VoxelArea:new{MinEdge=emin, MaxEdge=emax}
+	vm:get_data(data)
+	vm:set_lighting({day = 0, night = 0})
+	vm:get_light_data(light_data)
+	
+	for vi, x, y, z in area:iterp_xyz(emin, emax) do
+		for _, bubble in pairs(nearby_bubbles) do
+			if data[vi] ~= c_air then
+				local loc = bubble.loc
+				local loc_x = loc.x
+				local loc_y = loc.y
+				local loc_z = loc.z
+				local radius = bubble.radius
+				-- check outer bounding box first, faster than true distance
+				if x <= loc_x + radius and x >= loc_x - radius and y <= loc_y + radius and y >= loc_y - radius and z <= loc_z + radius and z >= loc_z - radius then
+					local inner_box = radius * cube_inside
+					if (x <= loc_x + inner_box and x >= loc_x - inner_box and y <= loc_y + inner_box and y >= loc_y - inner_box and z <= loc_z + inner_box and z >= loc_z - inner_box)
+						or vector.distance({x=x, y=y, z=z}, loc) < radius+math.random()/2 then
+						data[vi] = c_air
+						light_data[vi] = light
+					end
+				end
+			end
+		end
+	end
+	
+	if c_glow then
+		for _, bubble in pairs(nearby_bubbles) do
+			local loc = bubble.loc
+			if area:containsp(loc) then
+				local vol = math.floor(bubble.radius / 20)
+				if vol > 0 then
+					for vi in area:iter(loc.x-vol, loc.y-vol, loc.z-vol, loc.x+vol, loc.y+vol, loc.z+vol) do
+						if area:containsi(vi) then
+							data[vi] = c_glow
+						end
+					end
+				else
+					data[area:indexp(loc)] = c_glow
+				end
+			end
+		end
+	end
+	
+	--send data back to voxelmanip
+	vm:set_data(data)
+	--calc lighting
+	vm:set_light_data(light_data)
+	vm:calc_lighting()
+	vm:update_liquids()
+	--write it to world
+	vm:write_to_map()
+	
+	if mapgen_test_path then
+		mapgen_test.log_time_stop("bubble_caves")
+	end
+
+end)
diff --git a/bubble_caves/mod.conf b/bubble_caves/mod.conf
new file mode 100644
index 0000000..a444fac
--- /dev/null
+++ b/bubble_caves/mod.conf
@@ -0,0 +1,4 @@
+name = bubble_caves
+description = Inserts foamy spherical bubble caves in a layer underground
+depends = mapgen_helper
+optional_depends = mapgen_test, df_underworld_items
\ No newline at end of file