Workshop (Secret Mine)
From the Super Mario Wiki
The Workshop is a room inside the Secret Mine in Luigi's Mansion: Dark Moon. The Workshop is accessed by taking the north door in the Workshop Landing. The Workshop has many objects and tools scattered around the room. There are large pieces of conveyor belts and there is also a machine that shoots bombs.
In Across the Chasm, Luigi cannot enter the Workshop due to heavy snow taking out the power to the area and disabling the Strobulb sensor. He also cannot enter it after restoring power due to said snowstorm trapping him inside the Maintenance Room. In Chilly Ride, Luigi needs to enter the Workshop to confront the Shrewd Possessor that has the fifth piece of the Dark Moon.