Dens of Dying
From WoWWiki
The Dens of Dying are made up of two caves which are themselves each called Den of Dying. The area is located east of Bor'gorok Outpost in the northern part of the Borean Tundra.
The dens of dying are a sacred place to the magnataur, it is where they go in their old age to die.[1]
Trivia
The achievement 
Explore Borean Tundra lists this area as "The Dens of the Dying".
