Le Galera

"The prison of Le Galera has existed, in one form or another, since the days of Nero. Christians were persecuted here until Constantine, and native Salirosans for centuries after. Pirates, fascists, and terrorists have called these halls home till the ends of their days. Now, its primary demographic is Medician revolutionary."

Le Galera is a military base and prison in Just Cause 3.

Description
It's a military base and one of three prisons in Medici. This is the most south-eastern location in Medici and it's quite far from the mainland.

It is also stated in the in-game map that this place was originally constructed by Ancient Rome to serve as a Prison.

Strangely for a settlement of this kind, there is what appears to be half a Centcom tower fixated into the rock there. You can still go in the non rock half, and it behaves like a normal Centcom tower that has the computers, the stairs and the roof.