Avernus Fortress (Patreon)

286 x 230 @ 75pps

If your players ever want to attack a Devil fortress on Avernus.

As you can see it is a heavily modified version of Candlekeep, which typing it just pops an idea into my mind. It can be the hellish mirror of Candelkeep on this plane. Both fortress may be linked in some way, one being the keep of open Knowledge and the other of dark secret forbidden knowledge.

Your players could strike a deal or contract with those dark inhabitants to gain access to lost knowledge or even to open a (temporary) portal (south asset in the courtyard) ) to Candlekeep and be able to visit the material plane for a limited time (buy gear and magical items for example).

Another idea is that the center tower is the tower that controls all the chains that hold Elturel to Avernus and in the darkness binds it. Taking control of the tower could allow PCs to release Elturel.

This fortress can also replace Zariel's Flying Fortress or it can be a (very very) small Bronze Citadel.