Ancient Prison

Ancient Prisons are generated structures found naturally in The Overworld.

Generation
Ancient Prisons generate naturally on the Overworld surface. They are the rarest generated structure in the game; even rarer than the Woodland Mansion. They can spawn in any biome at any distance away from spawn.

Structure
The Ancient Prison is a simple structure. It is a 5x5 building with a hollow inside of 3x3. The walls consist of Stone Bricks (some of which may be Monster Egg), Iron Bars, and JackO'Lanterns. The floor is Stone Bricks.

There is a hole in the middle. The drop can range from 8 blocks to 23 blocks. At the bottom is the Herobrine Chamber structure.

Miscellanious

 * Hostile mobs have a slightly higher spawn rate near Ancient Prisons.
 * While Ancient Prisons can generate anywhere in the Overworld, they have a larger chance to generate on islands in the middle of an Ocean.