Passwall

A covert way in or out of Luthadel — a tunnel, a rope-hoist over the wall, a hidden door in the masonry. Felt explains to Elend that the Lord Ruler's interrogation regime made these the lifeblood of the skaa underground, that most have shut down since the start of the siege, and that the few still running are now letting people out of the city rather than into it. MB1:WoA:Ch 42