Stronghold

Strongholds are Generated Structures added in Update 0.9.0. They are the rarest generated structures in Minecraft Pocket Edition.

Generation
Generally only a few Strongholds, often just one, is generated in a World, making them hard to find. Sometimes they are generated in connection with a Village well.

As Update 1.0.0 it is possible to be located using the Eyes of Ender.

Exterior
Almost no outward indications exists, making them hard to find. However sometimes the Player can dig around a Village Well and locate the Stronghold. Sometimes even a door exist at the bottom of such a Well.

Rarely, the Stronghold will intersect with an Abandoned Mineshaft.

Interior
Strongholds vary in size but are generally large and complex like a maze, containing multiple rooms often with walls of Iron Bars, corridors, Libraries, stairwells, fountains, dead ends, and other features. Strongholds are lit by enough Torches to provide visibility in most areas, though not enough to suppress Mob from spawning.

They are mostly built out of Stone Bricks, Mossy Stone Bricks, and Cracked Stone Bricks. Some of these blocks are Monster Egg (AKA Silverfish Stone) which spawns Silverfish.

Of the more essential structures within a Stronghold are the End Portal room, and one or two Libraries with Loot Chests. The Libraries might contain several hundred Bookshelves.

Loot
It is possible to get loot from Chests present in Strongholds. They are:

Storage room Chests

Library Chests

Slab Altar Chests

Trivia

 * Strongholds are by far the biggest Generated Structures, often being larger than Villages.
 * Bug: There was an Android-exclusive bug in which Strongholds could not spawn.
 * If a Player leaves a World where there was supposed to be a Stronghold, it would crash the game.
 * In the Beta Version of Update 0.16.0, it was impossible to create a World with Strongholds at all, the game would crash and even deleting the World was impossible.
 * As of Update 1.0, Strongholds generate randomly across a World, even as far as the Far Lands, instead of exclusively underneath Villages.