From the Super Mario Wiki
The Jungle Exhibit is one of the various exhibits/rooms found in Treacherous Mansion in Luigi's Mansion: Dark Moon. Located at the bottom right of the map, it is accessed via the East Gallery to the left or Grand East to the north. There is also an E-Gate in a cave past the waterfall that leads back to the Front Entrance. The Jungle exhibit may be a possible representation of the Haunted Towers, due to the vegetational designs, and the mansion and ghosts tracks that play when inside the exhibit.
In Double Trouble, one of the two Toads trapped in the mansion is held in a painting stored in this room. However, a Flytrap and two Greenies with spears have to be defeated before the Toad can be freed.
In A Train to Catch and all later missions, Luigi can take a Bulb from the Study to the Jungle Exhibit to reach the top of the room. Up here he can use the Gold Berry to make coins appear; collecting these will reveal a treasure chest with a gem inside.