For you who dont know, there is a secret realm in minetest: floatlands
The realm is disable as default, but you can enable it by adding:
mgv7_spflags = mountains,ridges,floatlands to minetest.conf, or use the attached mod.
This works in mapegen v7 (the pictures are taken in minetest 0.4.15)
The islands can be really huge, and appear at the height 1280 as default
Helpful commands to get up there:
/grant singleplayer all
/teleport 0 1280 0
https://forum.minetest.net/download/file.php?mode=view&id=9465