Study (Gloomy Manor)
From the Super Mario Wiki
The Study is a room in the Gloomy Manor in Luigi's Mansion: Dark Moon. This area can only be accessed by using the bed in the Bedroom. The Study has a desk with multiple papers and an inkwell with a quill pen. Pulling off the curtains in the Study will cause a Gold Mouse to appear. There is a picture of a gem behind some drapes and a fireplace near a long carpet. Under the carpet is a switch that will turn off the fireplace, which acts as an alternate entrance to the Studio.
During Gear Up, Luigi needs to go to the Study to search for one of Slammers that took a gear from the mechanism in the Foyer. In the same mission, Luigi will also need to use the fireplace to make his way into the Studio. In Sticky Situation, the Study might be one of the rooms covered in spider webs.