Laundry Room (RIP Suites)
From the Super Mario Wiki
To access this room, Luigi must get rid of the vending machine that is south of the room with his Suction Shot. The first time Luigi is inside, three Goobs will be there. Two of them will be tossing toilet paper and the other will have a towel on its head.
Inside there will be a bunch of shelves with cleaning supplies, a sink, two washing machines, and a dryer. In the northwest side of the room is a vent that has a gem inside. If Luigi uses his Suction Shot on it, he will be able to go inside and get the gem. Opening up the middle washing with the Suction Shot reveals a Golden Goob. On the left side of the room, on top of the shelf is a stack of Bills. There are two Gold Bars underneath the sink. Opening up the left washing machine reveals a few coins.