Shadow Hold, located in western Felwood, is the main dwelling of the Shadow Council. It is a gigantic subterranean labyrinth roamed by Jaedenar warlocks and their demonic pets.
Night elfArko'narin is being held captive inside as well as her close friend, a human by the name of Trey Lightforge, who later turns out to have been tortured to death.
The layout of Shadow Hold and the presence of several named mobs suggest that Blizzard likely considered making this an instanced dungeon, but for some reason decided to make it a unique, uninstanced microdungeon instead.