Access to the Labyrinth is in the Path to Burial Temple behind the monoliths.
When you enter Scy's Lever Labyrinth, you won't be fighting anyone other than yourself.
There are 7 rooms with two levers each. Choose the correct lever, and you will move along without penalty; however, if you choose the incorrect lever, you are inflicted with +5% Vitae. Your final decision will either get you in front of the judge, where you will be cast out with only the vitae holding you back, or you will be sent back to the beginning to receive your reward of 20 free levels.
The Labyrinth can only be completed once per week.