The Royal Quarter of the Undercity contains the throne room where the Dark Lady Sylvanas Windrunner, and her general the dreadlord Varimathras control their burgeoning empire of undeath. It is protected by a squad of elite Royal Dreadguards. The entrance can be found in the Apothecarium adjacent to the green sludge moat.
This is also the home to the Battlemasters, the NPCs who provide a means to access Battlegrounds.
After the Battle for the Undercity, Varimathras is replaced by Bragor Bloodfist.