The Deadwind Pass Crypt lies behind the tower of Karazhan, in the cemetery at Morgan's Plot. 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. It is interesting to note that using WoW Map Viewer you can see that the crypt runs under Tranquil Gardens Cemetery in Duskwood. This might play a role sometime in the future, or could be a complete coincidence. This area used to be accessed via dying close to the gate and running through it, but this was changed in Patch 2.0.