There are two secret treasure rooms in Luigi's Mansion that you can access to load up on gems and money:

- The first one is located on the first floor, in the south-west corner of the Mansion. After you have sucked in the candle-carrying butler, examine the room with your Game Boy Horror to find a mouse hole. Press A to activate it and go inside to enter the treasure room.

- The second treasure room is accessible from the roof top. Use the elevator in the toy chamber to get on the roof, the go all the way to the right and climb up on the chimney. Fall down and you will land in another treasure room.