The Royal Coffers is a secret location in Luigi's Mansion 3 that is found on the first level of Castle MacFrights. It is north of the Coliseum Hallway. The green gem can be found here.
Near the end of the Coliseum Hallway, there are some tapestries of King MacFrights. Luigi must use the Poltergust G-00 to pull off the largest tapestry, depicting a complete image of the king. Luigi must then use the Dark-Light Device to reveal a secret door in the wall. Once the door is revealed, Luigi may enter the Royal Coffers, earning the Achievement "Found the Royal Coffers". Inside the room, there is a torch on the wall, four bronze statues of the king, a large pile of Coins and Gold Bars in the middle of the floor and the green gem in the center.
Names in other languages
||Sala del tesoro