Cellar (Luigi's Mansion 3)
From the Super Mario Wiki
Upon first entering the room, a Goob with a shield jumps out of a barrel. Luigi must use the Suction Shot to break the Goob's shield. After defeating that Goob, two Oozers and another Goob with a shield appear. On the east side of the room is a locked door. Luigi needs to find the key to open the locked door which leads to the Antechamber.
There are four huge barrels on the north side of the room. The three barrels on the left are laying on their sides, and the barrel on the right is standing straight up. Luigi can use the Suction Shot to open the three barrels that are laying on their sides. The first barrel has a bunch of tomatoes inside, but it also has a secret entrance into a part of the Stairway. This area can only be accessed through the Cellar. Inside the second barrel is the key to unlock the door leading to the Antechamber. Inside the third barrel are a bunch of rats and a secret path into the fourth barrel. Going into the fourth barrel leads Luigi to a ladder, and at the top is the blue gem. The fourth barrel also has a crack that Luigi can peek through to look inside the fourth barrel. There are a few smaller barrels in the room as well.