The Boss gives Ink free reign over the catacombs under the Cabaret Royale. He realizes the man has certain "urges" and indulges in them.
No one really knows if the area underneath is more extensive than it shows, since some exits were walled up some time ago. To access from the Cabaret, you must take the elevator down. It gives it a certain less sinister feel to it. Customers think it is just a way down to some storage or offices.
Once down there, there are only 3 other ways to get out (not counting going back up in the elevator). There are two ladders that lead up towards the surface. They are hidden extremely well and are narrow, making traversing them a tight fit for someone like Ink. There is also one exit to the other tunnels that riddle the Dock area. The entrance there is heavily secured; anyone passing through there are those loyal to the Boss or to Ink.
The area includes 2 play rooms (aka torture chambers) where Ink toys with his prey or teaches others a lesson they won't forget or even live through. The corridors are a maze, designed to keep folks disoriented and slow them down should someone be where they shouldn't or if an escape is attempted.
Passageways also contain sensors, which are set in varying directions, heights, etc. It keeps most people from accessing the area and moving easily.
The passageways are very dungeon-like. They look similar to this:
The map of the area is below: