By Bixyl Shuftan
Getting to the location I found on the Destination Guide, there were a couple signs telling people to walk around, one in English, one in French. They just had to click on the ground, wait for a red cube to rezz, and then "sit" on it. Just walking about, one looks like they're floating about a foot over the place. Once you have the red cube, you can walk about normally on the ground, even on the underside of the sphere.
The notecard suggested similar spheres could be easily made with a different environments in mind, and with close to three times the surface area of a flat sim, "it is so a not insignificant saving of space." The place was made by Freeloops Zanzibar, with Slove Mode designing the surface walking script. Others involved included Gizmo Tyrant, Loda Denfu, Coxigrue Borgin, Chikami Resident, and Abracada Dreamscape.
Citysphere is in SL9B By Us1 (134, 115, 2130). In January, it was advertised as running "throughout the month," but is still up.