Octagon

The Octagon was a huge magical prison located in the City of Brass in 1367 DR.

Description
True to its name, the Octagon was in fact shaped like a giant octagon.

Activities
The Octagon could easily hold up to 10,000 prisoners at any given time. Each prisoner was kept locked within their own cubed cell of solid basalt that sealed magically around them, leaving only a tiny slit for air and to pass food through. Impervious to attacks, these cells could only be opened by the efreeti prison guards.