Perpetouss Keep

Perpetouss Keep is an imperial base southwest of the Cauthess Rest Area in Duscae in Final Fantasy XV. It is unvisitable and quite small, though there are some items outside it. The location may be related Omega, as the author of the Ω-Files appears to be someone from a unit called "Perpetouss Troop" who works as a researcher for Niflheim.

The Pen is Mightier than the Sword
This quest for Vyv Dorden becomes available after completing "A Place to Call Home". Vyv wants three photos of imperial bases in Lucis: Formouth Garrison (Leide), Tollhends Stronghold in Cleigne (north of Old Lestallum), and Perpetouss Keep in Duscae. Each picture is part of a subquest that needs to be selected manually in the main menu to activate its waypoint. The player may have to engage imperial troops in each area. Completing the quest yields 4,000 EXP and 20,000 gil.