Full Synchronisation Requirement - Do not be detected
Go forwards, and head up the staircases and into the cave entrance. Keep heading straight through until you reach the hidden city at the end of the corridor.
Before you start exploring, keep in mind that for full synchronisation you need to stay as far away as possible from the Templar riflemen, as they’re the only enemies in this area that can spot you and ruin your optional objective if you avoid the streets and play smart. You can of course however make use of the crossbow or poison to take them out from a distance if necessary, or just sneak up behind them and put the hidden blades to work.
Your objective for now is to reach the colossal spire of rock to the southwest, located in the middle of the city. On the west face of it, there’s a climbable wall. Head up this way, then turn left and hop across the two wooden beams, and then go to the right and climb up the wall. Take another right, and jump to the ruined bridge. Work your way around the tower, looting the chest on the way, and take the beams until you can jump to a climbable wall. Once you reach the top, shimmy along to the viewpoint ledge. Climb up and synchronise, as you’ve been doing at similar ledges elsewhere.
Either climb down in the direction of your new objective, or leap off into the hay below. Continue to keep your distance from the riflemen, and when you reach the search area, use Eagle Sense. Scan all of the golden-glowing citizens in the street, and one will become marked and run off. Follow her, and confront her to end the Memory.