Under The Stairs is an unofficial location in Five Nights at Treasure Island.
It is a small crawlspace underneath the stairways. In the room you can see brick and stone as well as some small boxes. There is a Mickey Mouse mug sitting on one of the boxes. There is a vent that leads to the Meat Freezer as well.
Under the Stairs is a reference to a location in Luigi's Mansion:Dark Moon named the same name.