Board Thread:Questions and Answers/@comment-6342763-20130305115950/@comment-1429792-20130305145712

Night486 wrote: So Muken is the eight level of underground prison, and that's where Aizen is, right?

Correct

Also it is underneath First Division's barracks.

Also correct

But weren't the barracks destroyed by Juhabach? Yes, but they were above it, while Muken is deep underground. The barracks being routed has no real effect.

Also, if Unohana and Zaraki were fighting inside Muken, where was Aizen? It is unknown exactly where in Muken he is, but it was stated to be an extremely large area.