From the Super Mario Wiki
The Ancient Exhibit is a location in Treacherous Mansion in Luigi's Mansion: Dark Moon. Located in the north east of the mansion across multiple floors, this room is an exhibit based on Ancient Egypt and uses elements (like music) from the Old Clockworks.
There's one door to this room, found on the 1st floor to the south and leading down to Grand East. On this level of the Ancient Exhibit is a giant Egyptian style statue with two Strobulb sensors for eyes, a palm tree and some other plants in sand and a ramp leading down to the basement level.
On the basement level of this room are multiple sarcophagi, these are occupied by Mummies in mission E-2. There's also an E-Gate located behind the breakable stone mouth of the huge statue to the north.
The top level of the room has multiple ledges and Bulbs including a gold one.
During Double Trouble, Luigi explores the Ancient Exhibit and opens an E-Gate by breaking the wall in the basement. He also fights several Mummies here during this mission. The torches found here are used to light logs needed to melt the ice in the Ice Age Exhibit.
In Paranormal Chaos, the Ancient Exhibit is filled with ghosts including more Mummies.
In Terrifying Invasion, the Ancient Exhibit may be one of the rooms infested with ghosts.