Tunnel
In Assassin's Creed: Brotherhood, Niccolò Machiavelli shows Ezio a tunnel network 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 II have the letters SPQR 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.
The tunnels lead too places such as Tiber Island hideout, the Colloesum and the Brothel which his sister and mother run, and other landmarks and places, a intresting note would be that Ezio cant visit a landmark before he re-inovates It.