Undermountain Overview . This ancient dungeon started as a mine and dwelling of dwarves belonging to the Melairkyn clan . In the centuries since the dwarves were driven out it has been the home of drow , duergar , powerful wizards , criminal groups , and convicted felons . History . Aelinthaldaar , the capital city of Illefarn , was founded around - 8500 DR and first started to dig crypts in the area . The ancient dungeon itself started as a mine and dwelling of dwarves belonging to the Melairkyn clan that formed an alliance with the elves of Illefarn . In the centuries since the dwarves were driven out it has been the home of drow , duergar , powerful wizards , criminal groups , and convicted felons . The most famous of those to control the halls of Undermountain was Halaster Blackcloak , the Mad Mage . He and his apprentices explored the ruins and laid claim to many areas . Over the next thousand years they populated these areas with various monsters , magical experiments , numerous portals and traps . Around 1306 DR the City of Waterdeep started exiling convicted felons to the depths of Undermountain . Various criminal groups use portions of the ruins as their headquarters as do followers of evil gods . Halastar ’ s death in 1375 DR and the earthquake that accompanied it not only altered terrain but also upset the balance of power among the various groups . It was barely ten years later when the Spellplague tore through Faerûn and once again drastic change came to Undermountain . Many of the numerous portals in the ruins were destroyed cutting off entire levels . Other portals were warped and seemingly granted access to heretofore unknown levels . Also it is feared that pockets of Spellplague may still exist in Undermountain . Undermountain & Halaster Blackcloak . Over a thousand years ago , the wizard Halaster Blackcloak whirled to the base of Mount Waterdeep , called there from a distant country by chance or providence . Some say he hailed from the Cradlelands , the nearly forgotten empire that spread humanity across Faerûn , Kara - Tur , and Zakhara , from what is now the Plains of Purple Dust , a wasteland created by conflict between the gods . Whatever his origins , scholars record that Halaster brought with him the Seven , as his apprentices are known , and with their help and his power , Halaster summoned beings from other planes to build himself a wizard ' s tower . Halaster ringed his tower with a great wall set with lesser towers for each of his apprentices , and he created fields and farms to be worked by his apprentices and their servants . For a time , it seemed a good life for the Seven , but as the days wore on , they saw less and less of their dread master . Halaster continued to use fell creatures from other planes for construction beneath his tower , and he kept his dealings with them and the nature of the tunnels from the Seven . At length , Halaster ' s tunneling broke into the Underhalls , a complex of tunnels built by dwarves around a mithral mine beneath Mount Waterdeep . The dwarves who built the dungeons , the Melairkyn clan , had long ago been killed or dispersed , replaced by ofttimes warring duergar and drow . Halaster began a crusade against both races , participating in wild hunts through the tunnels with allies called from the Outer Planes . The duergar stubbornly remained until the mithral was largely mined out , but then they left the drow to fight Halaster and his minions alone . Halaster captured or killed the remaining dark elves , entrapping their souls for dark magic or twisting their bodies and enslaving their minds . When the last of the drow were defeated , Halaster Blackcloak tunneled on , ever downward , continuing his strange obsession with delving beneath the mountain . Finally , when Halaster was absent for more than a year , some of his apprentices ventured into his tower in search of the great wizard . They found traps , monsters , and tantalizing hints about power beneath the earth . Individually they plumbed the depths of the dungeons , encountering ever more deadly traps and more powerful foes . For their efforts , they were rewarded with riches and magic . When the Seven were reduced to five , Halaster appeared to his students and explained that he had built the tunnels to guard his experiments and treasures . He enlisted their aid to make his dungeons even more secure . What happened after that is unclear , but only one apprentice is known to have left Undermountain , and she fled the area , never to return . Halaster continued to live beneath the mountain , using it as a base from which he traveled to other planes and distant lands , entrapping strange creatures and bringing them back to live as prisoners or guardians in his home . In time , Halaster sought out magic to extend his life , and some say that it was these spells and items that finally drove Halaster beyond all reason . While before he had been obsessed and deranged , his quest for immortality seemed to drive him truly mad . While Halaster quested on other planes and sequestered himself in his tunnels , his tower fell into ruin . When Halaster was yet active in the outside world , his home was considered an accursed place , so settlers in the area largely left the crumbling tower alone . In time , the city now known as Waterdeep came to huddle against the mountain and reach down to the harbor . As the city sprawled outward , it reached and encompassed the ruins of Halaster ' s home . Undermountain was known to these early settlers , and they often punished criminals by sending them into its depths . So it was for many years until an adventurer named Durnan delved into the depths beneath the tower and returned , laden with riches , to tell the tale . Durnan demolished the last remnants of Halaster ' s above - ground abode and built an inn over the well he had used to descend into the depths . He called his inn the Yawning Portal , and Durnan works there to this day , serving patrons and inviting the brave or the foolish to try their hands at the halls of Undermountain Entrances & Exits . The halls of Undermountain are linked to the surface world in countless ways , both physical and magical . Halaster uses his network of portals to bring in monsters from all across Faerûn to restock his dungeon . He also uses portals to draw adventurers into the deeper regions , rarely explored , and to give the occasional lucky adventurer an unexpected escape . Some of the notable physical links are described below . Levels of Undermountain . Major Levels Sub - Levels