Tunnel

In Assassin's Creed: Brotherhood, Niccolo Machiavelli shows Ezio tunnels that he can use to travel quickly to any other tunnel entrance in Rome that he has repaired.

The tunnels, which are the equivalent of a fast-travel station in Assassin's Creed 2 have the letters S P Q R engraved over the entrance. When selecting the area in Rome where the player wants Ezio to go to, there is a brief cutscene of him opening the latch on the gate and entering, but the player is not able to travel in the tunnels themselves.