The Barrow Crypts are a series of 6 crypts in the Frozen Wastes. Their purpose seems to be to guard the bones of Maximus, a gigantic bone golem that adventurers enjoy collecting the pieces of, placing them in the phylactery, and summoning him, mostly just so they can tear him back apart.
There are 6 crypts, though they are mostly identical. Each crypt is managed by a single powerful Wight, that is cursed to old each bone, and if destroyed, will regenerate once Maximus has been destroyed and its bones returned to their resting places. Each crypt is also haunted by ghosts of dead adventurers that failed to slay the crypt's wight.
The center of the area contains the phylactery of Maximus, and when all six of his bones are placed inside it, the terrifying Bone Golem will manifest itself and begin to destroy and kill everything in the area unless it is itself destroyed.
There's also rumors of a mysterious Gauntlet of Terror... hidden deep within one of the crypts.