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The Red Door is a mysterious Blue Prince secret found in the Underpass — an area that you’ll only find on your own after a whole lot of exploring and puzzle-solving. The Red Door is the only noticeable optional direction you’ll encounter in the Underpass, the road that leads to the Underground Lever that unlocks Room 46. If you’re curious what’s inside the Red Door and how to unlock it, we’ve got the full guide below.
If you haven’t even found the Underpass yet, check our full Room 46 guide for details explaining how to access the Underpass where the Red Door is located.
How To Open the Red Door | Underpass Guide
The Underpass is the road that leads to the Inner Chamber where the Underground Lever is located. This lever opens Room 46 in the Antechamber — and you’ll need to reach this underground room to beat the game. The Underpass is mostly empty, except for a passage on the left side that leads into a hallway with a window outside and a locked red door. The red door has a red power box that is naturally deactivated.
- NOTE: To access the red door, you’ll need to be able to return to the Underpass at any time. To get all the rewards, you’ll want to move the minecart so you can easily access the switches in the Cog Wheel Room of the underground. You can access the minecart from the Tomb / Fountain / Precipice paths into the Underground.
To open the Red Room, you’ll need to divert power from the Boiler room in the main house.
- Underpass Red Door: In the Boiler Room, activate the steam boilers and turn the red pipes so power is diverted into the red box. The red box is on the ground floor of the Boiler room.
- You don’t need to fully power-on the boiler, you just need to follow the pipes from the red box and sent steam power to it. When the box lights up, you’ll power-up the red door.
Go down to the Underpass after sending power to the Red Box in the Boiler room. If you have, the red box in the Underpass will be lit up and the Red Door will open.
What’s In The Red Door?
The Red Door conceals a path that leads to the upper level of the Cog Wheel Room. There are two rooms on the upper level with clues and permanent rewards you can collect.
- Use one of the Cog Wheel Room controls to raise the bridge so it is reachable on the top level. We highly recommend moving the Minecart so you can easily move to different positions without spending steps in the Reservoir.
- Raise the bridge, then move the upper bridge so it is connected to the 7 o’clock position. That’s where the stairs on the upper level take you.
There are two rooms you can reach from the Red Door path. You can reach one on the upper-right and one on the upper-left depending on how you place the bridge.
- Upper-Right Room: Leads to room with glass marking spots on the Reservoir. Solve the puzzle in this room to earn +2 Allowance permanently.
- The window is marked at different positions: 14 (Full), 13 (Dock Level), 6 (Entry Level) and 0 (Full Drain).
Remember those water level positions. They’ll be important for solving the huge endgame puzzle.
- Upper-Left Room: The upper-left room has a locked gate. Think back to an important date marked on all the documents in the house.
- GATE LOCK SOLUTION: [M-A-Y-8]
- Press the red button after inputting the code to open the gate.
- This room contains a Gem and Red Letter #1. You’ll also find the Treasure Trove Blackprint — a special room that gains +5 Coins every time you place it. Each time you draft the Treasure Trove, more treasure will be found inside.
And that’s all the valuable rewards you’ll find in the Underpass. It’s a rewarding location but also totally optional — some of the clues, like the Reservoir water levels, are easy to discover on your own with experimentation. Still, we can’t turn down a secret blueprint or a little more allowance per day.
