Fort Boubastos (Location)
A Roman fort in Haueris Nome that you'll raid during the Fighting for Faiyum Quest. You may want to wait until then- it's not the sort of place you want to conquer twice.
The Fort's a giant place, and halfway through rebels will attack, throwing a wrench into any careful plans, but there's still room for tactics. Do scan thoroughly before proceeding- it'll help you keep track of enemies once things go crazy. It'll also pinpoint the local treasures- three around the commander's quarter in the south building, one north near the not-quite-central watchtower.
Start at the north west edge of camp- there's a captain here you'll want to dispose of.
Some boken fencing in the bushes provides a good angle of attack.
Kill him and nearby enemies to get access to the underground tunnel across the way.
This leads to the prison area- you can either free the prisoners now (adding to the chaos, but probably getting most of them killed), or later (safer, but less helpful).
By this point, the rebel attack will have begun, but there should still be some high level targets in the area.
Keep stealth as long as you can, but once your cover's blown, use aerial attacks, smokescreen, and ambushes to keep the upper hand.
Keep at it until the enemy forces have been cleared. Be sure to use your adrenaline whenever it fills to speed the extermination process.
You can then recover the area treasures. The first is on the commander's table.
Note the large spiked door in this room. Two treasures are behind it, but you can't bust that door. Instead go out over the wall, and come at them from the other side, through what may or may not be stables.
Two chests are inside.
The last is just inside the door of that watchtower, on the ground floor. Snagging it completes the location.