Assassin's Creed Revelations Walkthrough Part 6 – A Warm Welcome

You will awaken back on the Animus Island and Subject 16 will explain a few more aspects of the Animus's fail-safe program. He also explains that he is doing what he can to keep it distracted while Desmond explores outside his particular partition. Once again, take some time and wait as you will hear Rachel and Shaun talk a bit. When you are ready, head on forward into the portal again.

Full Synchronization is achieved by not wandering far from Yusuf

On the other side you have a cut scene with Prince Suleiman. After that you will meet your local “guide” and cohort, Yusuf Tazim. Just walk and keep close. This tour will lead you through Constantinople (or Istanbul depending on who you ask), to the Assassin's Headquarters.

En route you will encounter a few small waves of Templar guards. The first is a simple trio while the second is chased off by some mercenaries. Now keep to Yusuf. Just a short while later you will arrive at the entrance to the Assassin's Headquarters. Enter to finish out this part of the sequence.