Unearthed Arcana

Defenses Wrought of Mortar and Magic
Heroes need impregnable fortresses to assault, wondrous towers to explore, and majestic castles to protect. This book is stocked with everything needed to design any fortified structure imaginable, including:
Over 150 new magic items.
More than two dozen magical augmentations for stronghold walls.
Rules for magic portals, mobile strongholds, and trap creation.
Five complete strongholds, including maps, ready for immediate use.
Players and Dungeon Masters who want to create customized strongholds will find all the construction materials they need within these pages.
To use this accessory, a player or Dungeon Master also needs the "Player's Handbook."