Underrealm

The underworld. Hell. The seven hells. What have you.

There seem to be multiple hells/underworlds to Gaera Main (one Sirvix Malone hails from, one Malachias ruled, et cetera). I'm thinking the Underrealm is a bit different from just 'underground'--perhaps a plane unto itself. A number of nekogami's characters' BGs speak of the underrealm needing portals to get to the middlerealm/Gaera, which seems to support this.

Thoughts?