Crypt

There are several places in the realms known simply as Crypt.

Arathi Highlands
The Stromgarde Keep crypt in the Arathi Highlands is currently controlled by the Alliance faction of humans. It is tended by three caretakers, and is quite small compared to most other crypts in the realms.

Badlands
The Badlands crypt is located southeast of Hammertoe's Digsite, at the very apex of the hill behind Sigrun Ironhew. It is empty save for a grandoise crypt seat complete with an armored skeleton.

Western Plaguelands
The Sorrow Hill Crypt contains a lot of skeletal mages and scourge warders. You find it in Western Plaguelands, the southeastern way from Sorrow Hill. Judging by its location, it's speculated that this was the crypt that originally held the corpse of the necromancer Kel'Thuzad.

Deadwind Pass
This crypt lies behind the tower of Karazhan in Deadwind Pass, and is by far the largest of the crypts, stretching deep underground in a labyrinthine series of rooms, each more horrifying than the previous. One of the horrific rooms being the "Upside Down Sinners" -- A large water-filled room with dead people attached to chains, floating away from their attached chain slightly.

This area could be accessed via dying close to the gate and running through it, but this was changed in Patch 2.0