Garage (Luigi's Mansion 3)
From the Super Mario Wiki
The Garage is a location in Luigi's Mansion 3. It is found in the Basement of The Last Resort. It is a parking lot directly west of the Elevator Shaft and northeast of the Laundry Room. The red and white Gems can be found here.
After rescuing Professor E. Gadd, Luigi must escort him to the garage, where they discover Steward in his true, ghostly form. After Luigi defeats him, Professor E. Gadd walks back to his car to get a device he sets up in the middle of the lot. It becomes a portable lab, where Luigi can see a map of the hotel, play multiplayer, view collected ghosts and gems, and talk to the professor.
In the garage, there is a car with a hooded trunk. Luigi can pull off the tarp, then flash the green light with the Strobulb to pop open the trunk, revealing the gem. The red gem can also be found to the left of the garage in a caged area. Gooigi needs to walk through the chain-link fence, where he will find both the gem and a treasure chest. To get the gem, Gooigi needs to pull off the electrical box cover with a Suction Shot, then flash the light to break off the cover.
More treasure can be collected in the garage. There is a panel in the northeast corner Luigi can use the Suction Shot on to enter the elevator shaft, where the blue gem is. There is another panel in the southeast corner hiding a drain Gooigi can squeeze through to get to a ceiling light with Gold Bars. Other treasure can be found in dirt piles around the garage. There are also a few gold bars in a hole opposite the door which can no longer be collected after Professor E. Gadd sets up his lab.