To open the north door in Blue Prince , you need to reach the Underground route that leads to the Sanctum, then find and pull the lever for the north- facing Antechamber door. The north door is not opened from the Antechamber itself; it’s unlocked by a lever hidden behind the throne in the Throne Room, which is revealed through a secret floor plan somewhere on the estate.

What to do

  1. Get into the Antechamber by unlocking one of the estate levers first. The door you can open depends on which lever you found.
  1. Reach the Basement and Underground. One common route is through the Foundation using the Basement Key, and another is by draining the Fountain to access the second basement entrance.
  1. Work through the rotating gear / platform puzzle in the Underground until you reach the Sanctum.
  1. Pull the lever there to unlock the north-facing Antechamber door.
  1. Return to the Antechamber and enter Room 46.

Helpful detail

The puzzle chain usually involves moving the minecart out of the way first, then using the basement and reservoir access points to line up the rotating platform correctly. Several guides point to the same end goal: the north lever is in the hidden Sanctum route beneath the house, not in the main estate rooms.

One-line version

Find the hidden lever in the Underground Sanctum path, pull it, then go back to the Antechamber and use the north door.