[jrootabega]

Seems simpler to know exactly where the entrance is, relative to the entire building. You could build a hallway off it.

[jamestimmins]

This theoretically makes it usable in a smaller space, since you don't need a hallway to run around the entire ring.

[dsfyu404ed]

Getting a prisoner in or out would be like the Central Bureaucracy cube in Futurama.