Eryndlyn Eryndlyn was a drow city of more than sixty thousand in the Upper Underdark . Geography . Eryndlyn was located in caves beneath the High Moor in the Upperdark . Eryndlyn dominated the northern Undermoor tunnels ; the southern tunnels were home to derro and illithid s . Description . The limestone cavern of the city was dome shaped and more than two miles in diameter . A shallow lake lies in the center of the cavern was fed by two freshwater rivers and drained by a third . The rivers left large plateaus upon which the drow dwelt ; slaves often dwelt in caves along the shores of the lake . The city ' s three plateaus were each dominated by one of three religious cults : Lolth ites held the largest plateau , located on the western side of the city . Vhaeraun ites dwelt on the northeastern plateau , and the southeastern plateau ( which was often flooded ) was home to followers of Ghaunadaur . History . Background . Eryndlyn was founded by drow seeking to reclaim the ancient elven realm of Miyeritar . They were not particularly religious , so unlike many other drow cities , Eryndlyn was not devoted to one particular deity . However , as merchant clans grew to dominate the leadership of the city , cults to Ghaunadaur , Lolth , and Vhaeraun sprang up in an attempt to gain power . Each cult eventually consolidated their followers to one of the plateaus . Circa 1362 DR , House Yauntyrr was attacked and defeated . Many members of the house were killed ; others were taken in by Ched Nasad ' s houses ( such as Danifae Yauntyrr , who became a battle captive to Halisstra Melarn ) and yet other survivors fled into the Underdark . Zinnirit Yauntyrr , the house wizard , escaped to Sschindylryn , where he began operating a three - portal gatehouse until his death in 1373 DR . Silence of Lolth . About the time of 1136 DR , Jaezred Chaulssin established a hidden fosterage in the city under Tomphael Arkenrret under the guise of minor nobility . During the Silence of Lolth ( 1372 - 1373 DR ) the members of Jaezred Chaulssin brought the worshipers of Vhaeraun and Ghaunadaur together and helped to unite them against the weakening worshipers of Lolth . They decimated the followers of the Spider Queen drastically , leaving the western plateau in ruins . The followers of Kiaransalee who never managed to count a few outlaw drow among themselves were unable to find a foothold by 1372 DR . In fact , due to the strong existence of the other factions , backing a weak party like Kiaransalee ' s cult wasn ' t considered profitable enough to be attractive . Post - Spellplague . The Spellplague destroyed Eryndlyn , leaving it a blasted ruin . It had turned an earth node in the vicinity of the city into the deepest spellcave in Northdark . The citizens of the city itself though , had mostly abandoned the city beforehand in the face of outside threats after their civil war . For some reason , the major Jaezred Chaulssin fosterage under Tomphael Arkenrret was maintained and was still active there . Duergar from Gracklstugh began reporting earthquakes and explosions from the ruin in the area adjoining the city known as the Spellcaves - a cavern full of wild magic since Eryndlyn ' s destruction . Lolth , in the form of Danifae Yauntyrr , tried to use the Spellcaves as a focus to merge herself with the Demon Weave in 1485 DR , thereby becoming the new goddess of arcane magic , but the attempt failed and instead Mystra , thought dead for an entire century , appeared and warped the Demon Weave into a form more akin with her original Weave . Inhabitants . In addition to the drow , there were many orc , goblin , and troll slaves . Trade . Eryndlyn ' s merchants traveled far and even traded with surface merchants along the Sword Coast .