The Pirate Caverns is a special area accessed as the second half of Night 3. This area is where the 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 non-working elevator seen in one of the rooms.