The text of the sim says it all:
"WELCOME In CitySphere's World, a new conception of the world for much more pleasure!!! A city of 132 buildings distributed on a sphere, besides the originality of the decoration, which can be made at your own taste, the sphere possesses 3 times the surface of a sim, it is so a not insignificant saving of space!"
Click on the panel at the teleport point to get the required transportation, otherwise you will keep falling off the world... Taking pictures was a bit of a challenge!
The sim is rated Mature/Moderate