This crypt lies behind the tower of Karazhan in Deadwind Pass, in the cemetery at Morgan's Plot. It is by far the largest of the crypts, stretching deep underground in a labyrinthine series of rooms, each more horrifying than the previous. Easily the most horrific chamber is the "Upside Down Sinners" - a large water-filled room with dead people attached to chains floating upside-down, feet pointing towards the ceiling. The underground network of crypts contains other strange chambers as well:
* Well of the Forgotten
* The Pauper's Walk
* The Pit of Criminals
* Tome of the Unrepentant [sic]
* The Slough of Dispair [sic]
The bizarre layout and naming conventions of the crypt are unlike any other region, dungeon, or instance in the game. The purpose of the crypt is unknown - it may be a playground for developers, a testing site of sorts, an unfinished instance, or something else entirely. Some people speculate that is a lower portion of Karazhan, as some lore indicated Karazhan has a lower half. But upon further investigation the architecture does not match with Karazhan in the slightest bit, leaving a rather large flaw in their speculation.
This area could be accessed via dying close to the gate and running through it, but this was changed in Patch 2.0.
Also note that the region known as "The Slough of Dispair" [sic] is a reference to the popular game Doom's level of the same name.