Kyrenaika Roman Citadel (Location)
A giant Imperial fortress in the Green Mountains.
There are a number of secret entrances, but you're best off starting at the battlements anyway, so approach from the tower in the west corner.
Climb up and clear the area of guards. Note also the excess of arrows available here.
Climb to the room, and repeat the procedure with the tower directly east
Clear the battlements nearby- enough that you have a clean shot at the commander's office here (it'll also have a quest marker for 'Carpe Diem'
Come in over the roof, and assassinate your way inside.
Backstab the commander, and steal the treasure from his desk. The letter here also kickstarts the Carpe Diem quest
Sneak to the middle gate, either over the rooftops or through the buildings- the former is faster but riskier. The gate itself is a target rich environment- a captain on watch, and a treasure in the low building behind the gate, on the north side.
Slip inside the building and loot the red chest for treasure.
Step out and assassinate the gate guards, starting with the captain.
When they're down, climb up to the battlements and head toward the east half of the compound, for the last captain's quarters, and the next treasure.
The captain wanders around that same building a lot (seems too casual to call it a patrol). In anycase, wait by the rear balconies to get the drop on him.
Drag the body inside, and loot the red chest by the base of the ladder.
This room actually has a passage straight to the last treasure. Drop down to the basement-level hallway, partially obscured by the giant billowing curtain here, toward the northwest of the room.
Follow this passage to get to the basement of the target building, but you need to get to the top floor. Take two ladders up, then climb up the outside of the tower. There's a door back in on the northeast side.
Grab the final treasure from a white box here to complete the location.