How to reach the Mansion Underground in Blue Prince?

If you’re playing Blue Prince and wondering how to crack open the mysterious Underground area of the mansion, you’re not alone. This place is a core part of the game, packed with secrets, puzzles, and key progress points. Here's the fastest, easiest way to get you down there.
Step 1. Get the Basement Key First things first—you need the Basement Key. It’s always found in the Antechamber, and each new run places it right back there. Grab it early and hold onto it until you’ve used it to unlock at least one Underground door. Good news: once a door is opened, it stays open forever, even if you lose the key later.


Step 2. Pick Your EntranceThere are five possible entry points into the Underground. You can use any of them, but some are faster or easier depending on your layout and progression.

1. Foundation (Most Reliable)

• Once placed, it stays in the same spot every run.
• Make sure it’s placed near the Entrance Hall for fast access.
• Use the elevator inside to go straight down.
• Requires the Basement Key to proceed deeper.

Tip: Best pick if you're aiming for consistency and speed.

2. Fountain (Takes Some Setup)

• Drain the Fountain to reveal a narrow tunnel.
• A mine cart blocks your path—move it based on your intended route.
• Push or pull it strategically to access the Rotating Gear and North Lever section.

Tip: Great if you’ve already cleared the Fountain and managed the cart properly.

3. Cliffside (Needs Tools)

• Go through the manor grounds and down to the tunnel.
• Use a Power Hammer to clear debris and break walls.
• Leads into a side section of the Underground near the Foundation.

Tip: Best if you’re equipped and want to explore.

4. Tomb (RNG-Based)

• Unlocks randomly when drafting rooms.
• Unlock the Garage Door to draft the Tomb.
• Solve the Tomb puzzle (clues in the Chapel)..
• Connects to the same mine cart area near the Fountain.

Tip: Only use this if you’re lucky with your room draft.

5. Blue Flame (Endgame Option)

• Light all four Blue Flames on the grounds.
• An elevator appears. Use it to go to a hidden tunnel near the Chess Puzzle .
• Bring a torch or light source to make it through darker zones.

Tip: High effort, but cool if you’re going for full completion.
Step 3: Head to the Rotating Gear Area No matter which entrance you take, your real goal is to find:

• The Rotating Gear
• The North Lever

This area unlocks the path to Room 46, one of the game's key locations.

Once you unlock paths with the Basement Key or place the Foundation smartly, future runs become much faster. Invest the time early, and you’ll breeze through later.