This achievement is awarded after completing the following missions in Sequence 2 - The Crossroads of the World with at least 50% synchronization:
Memory 1 - A Warm Welcome
Memory 2 - Upgrade and Explore
Memory 3 - The Hookblade
Memory 4 - The View From Galata
Memory 5 - Advanced Tactics
Memory 6 - On the Defense
Memory 7 - On the Attack
For those of you going for
there are some videos posted below that should help you achieve 100% synchronization in each memory. The videos do not belong to me and I do not take credit for them.