Reliquary of Agony can be found right below Zeramas in Zul'Drak. This area is infested with Scourge and filled with pools of blight.

One notable undead creature, Gristlegut, can be found here. He gives the player, in which he thinks is a simple ghoul, quests and will also sell/buy things for them.

v • d • e Subzones of Zul'Drak Altar of Har'koa · Altar of Mam'toth · Altar of Quetz'lun · Altar of Rhunok · Altar of Sseratus · Amphitheater of Anguish · The Argent Stand · Crusader Forward Camp · Dubra'Jin · Dargath's Demise · The Dead Fields · Drak'Agal · Drak'Mabwa · Drak'Sotra · Drak'Sotra Fields · Drak'Tharon Keep · Ebon Watch · Frigid Breach · Gundrak · Heb'Drakkar  · Heb'Valok · Kolramas · Light's Breach · Mam'toth Crater · Pools of Jin'Alai · Pools of Zha'jin · Rageclaw Den · Rageclaw Lake · Reliquary of Agony · Reliquary of Pain · Thrym's End · Voltarus · Zeramas · Zim'Abwa · Zim'Rhuk · Zim'Torga · Zol'Heb · Zol'Maz Stronghold Zul'Drak category