This minecraft mod essentially just generates hundreds of different spheres in minecraft, out of different materials. You are able to set it so that you have open sky at the bottom so you just die whenever you fall, or you can have water. I’d suggest open sky unless you want to be building anything at the bottom.
The current version is v1.75 and it does not require any additional things to run.
Download here: http://cid-f4a929c2025618e4.office.live.com/embedicon.aspx/Minecraft%20Planetoid%20Generator%20-%20V1.75/PlanetoidMapGenerator.zip
Made by Seibai