The Pirate Caverns is a special area accessed as the second half of Night 3. This area is where Undying will start.
When the player enters Pirate Caverns, the game style changes to a point-and-click type of adventure game where the player clicks to go to other areas in the cavern. The player can enable a flashlight by pressing the space bar. The Face will also be a threat in this area.
The locations in Pirate Caverns consist of an aquarium, an area with some couches and an elevator, an office, a staircase, and a room with a piano and a treasure chest. There is an area that is not accessible as of the latest update, called Undying's Room. This room, and possibly others, could be accessed via the elevator seen in one of the rooms.