The Underground is a large basement area beneath the estate in Blue Prince and there are multiple ways to gain access. This is where the true meat of Blue Prince is found, and where the deepest mysteries are unlocked. You can’t open Room 46 until you extensively unlock large sections of the Underground, and the more routes you unlock to this area, the easier time you’ll have getting to Room 46.
The Underground is a series of rooms connected to the house. This area is not part of the house and remains the same as you progress. If you change a part of the underground, it will permanently change until you change it again — it does not reset.
The Underground leads to the Underground Lever that unlocks Room 46. We won’t talk about that here, instead we’ll go in-depth on every method for reaching the Underground. There are five ways inside, and you’ll want to unlock as many as possible for the best chance at beating the game.
For more help reaching the Underground Lever and Room 46, check out our full Room 46 guide here for extensive details on the big puzzle that leads to the first ending of the game.
The Basement Key | Underground Access Guide
The Basement Key is the first and most straightforward access to the Underground.
- Basement Key Location: The Basement Key is found in the Antechamber — the empty white room at the top of the house on any given daily run.
NOTE: The Basement Key is LOST after the end of the day. But it will permanently unlock doors it is used on. If you can’t reach the two doors it unlocks, try to place the Basement Key in a Coat Check room for storage.
Reaching the Antechamber is its own difficult challenge. Learn how to unlock the Antechamber doors with our full lever locations guide here.
The Basement Key is used on two doors — and as stated above, once the doors are unlocked, you won’t need the Basement Key again. If you unlock both doors, you can lose the Basement Key.
- Basement Key Door #1: Draft the Foundation room in your house — this is a room that is permanently placed once drafted. There’s a lift in this room that leads to the Underground. The red door is unlocked with the Basement Key.
To reach the lower level of the Foundation, you must activate the hidden lever on the outer wall of the Foundation. Open a doorway facing the side of the Foundation with the lift (the side with no doors) to reveal the hidden lever. Using it will permanently lower the lift and give you access to the Basement.
The Basement has its own elaborate puzzle. To reach the Underground from the Basement, you must move the carts to create a bridge leading to the switch near the Basement Key Door. This leads to the Reservoir and has easy access to the Cog Wheel Room.
- Basement Key Door #2: Found at the bottom of the Fountain in the front yard of the house. Draft a Pool Room to add the Locker, Sauna and Pump Room to your roster. Draft the Pump Room and adjust the water level to drain all the water from the fountain.
- This is a permanent change until you change the water levels again at the Pump.
This approach leads to the opposite side of the Reservoir. You’ll find a round Sigil Room and be able to move the Minecart to make access to the Cog Wheel Room much easier on future visits.
The Power Hammer | Underground Access
The Power Hammer is a Contraption made at the Workshop that unlocks permanent access to the same Basement as the Foundation Basement Key path. It’s also the easiest, most consistent method for going straight to the Underground.
- Power Hammer: Draft the Workshop — an uncommon room — and combine three items to create the Power Hammer.
- Combine the Sledgehammer + Broken Lever + Power Pack.
With the Power Hammer crafted, you can now bust open the path to the Underground.
- Power Hammer Path: Build the Power Hammer and use it on the blocked-up doorway near the stone balcony in the Grounds area. This is the same general area as the four blue fire braziers.
- Smash through the doorway to reach a Mine Shaft. Smash through the bricked wall to reach the Basement.
The Basement is the same area you’ll reach through the Foundation Basement Key Door. You’ll need to solve the same puzzle with the carts to reach the button and reveal a hidden path to the Reservoir.
The Tomb | Underground Access
One of the rare methods for reaching the Underground is by passing through the Tomb. The Tomb is a random Outer Room that is only accessible once you’ve unlocked the West Gate. Learn how to open the West Gate here.
- The Tomb Path: Select the Tomb as your Outer Room choice through the West Gate. Down below, there are statues holding different items. By using the statues and moving the arm position in the correct order, you’ll unlock a hidden path.
- 1. Hoe (Gardener)
- 2. Bread Shovel (Chef)
- 3. Pitchfork (Farmer)
- 4. Chimney Brush (Chimney Sweep)
- 5. Broom (Maid)
- 6. Riding Crop (Horse Rider)
- 7. Mitre / Mace (Crown)
- After interacting with the statues in this order, go down the stairs and interact with the Scythe statue.
This unlocks a path leading to the back of the minecart. This is the same area as the Well / Fountain Basement Door path. And there’s one more method for reaching the underground.
The Precipice Shortcut | Underground Access
The final shortcut is found through the Precipice — another optional underground location you can unlock. The Precipice can be unlocked by lighting four fires by interacting with four hidden gas valves. Check out our full guide here.
- HOVEL: Outer Room accessible from the West Gate. Found in the back of the room.
- SCHOOLHOUSE: Outer room accessible from the West Gate. Found behind the large boiler in the center of the room.
- GEMSTONE CAVERN: Permanent upgrade room found near the camp on the exterior grounds that is unlocked by solving the V.A.C. Puzzle in the Utility Closet Breaker Box.
- Apple Orchard: Permanent upgrade room found near the camp on the exterior grounds. Unlock by inputting the code on the lock — the code is found in the Dark Room on a photo. The code is [11-28].
Once the Precipice is unlocked, you can open the shortcut in the Underground. You’ll need to access the section of the Underground through the Tomb or Well / Fountain path to reach the round sigil room.
- Precipice Shortcut: Craft the Burning Glass item in any Workshop, similar to the Power Hammer. Combine the Metal Detector and Looking Glass to get this item. It can light candles and fuses.
- Go to the Underground Sigil Room — it’s accessible through the Tomb underground door or the Basement Key door in the Fountain. Light all the candle stands in this room.
Lighting all the candles will cause stairs to lower, revealing a hidden path at is permanently unlocked. This path is handy because you don’t have to rely on the Tomb spawning and can refill the Fountain with water in the Pump Room, so you can now divert water to a different location permanently.
