Castle keys are a set of three items in Luigi’s Mansion 3. They’re used to open various doors on the sixth floor, at Castle MacFrights. Each one can be found in the room where the locked door is, but they’re well hidden. There’s one in the cellar, one in the cage lift room and one in the dungeon. If you get stuck trying to find them, this guide will show you all Luigi’s Mansion 3 castle key locations.
Cage lift room key location
When you reach the cage lift room, go down to the bottom. Shine your darklight onto the right wall, and it’ll reveal a hidden door. Go through it, and you’ll end up in a room with a bunch of crossbows blocking passage. Pull the left ball with your vacuum cleaner, then send Gooigi to the other side to pull the right ball. The platform will collapse, allowing you to get to the other side yourself. You’ll find the chest on a platform there. Once you return to the cage lift room, you’ll have to fight a bunch of red box ghosts, so be prepared.
Cellar key location
You’ll probably find the cellar key while fighting the shield ghost. If not – it’s in the middle barrel in the cellar. You’ll need to break the lid in order to reach it – you can use your plunger extension to do this.
Where to find dungeon key?
The dungeon key is plainly visible when you enter the room, but it’s in a cell. In order to reach it, you’ll have to summon Gooigi and have him pull the ball on the left to open the cell. Once you go inside and pick it up, the cell doors will close and a trap will spring. Gooigi will have to defeat the two ghosts that appear, so he can open the door again and let Luigi out before it’s too late.