The Assassin's Tombs will appear as an Assassin Icon on your main map after the completion of Novella's secret sequence 4. This will be the fifth and final tomb available to you and is located in Venice.Find the entrance at the Icon and navigate through the tomb inside the Santa Maria della Visitazione to find the Catacomb. This trophy will sound after you obtain the Seal of Leonius from the assassin's final resting place and exit the area.

Here is a video for you to follow when your trying to unlock this trophy.
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