Great Door The Great Door was a massive door hidden on the outskirts of Waterdeep on the Sword Coast North . It served as a " gate " to the planes . Defenses . The Great Door was constructed inside a huge pit in the ground , covered over with an illusion of solid ground . After it was tampered with , the Door could shoot bolts of magic at those outside , and release monsters from other planes . It could also levitate into the air , tearing up the ground with it . Description . The Great Door was a colossal pair of doors set into the cliff - face of the pit , bearing many human and monstrous faces and topped by a statue of a winged , dragon - like creature that looked down on those below . Powers . The Great Door contained a " gate " that unlocked an interdimensional wormhole to the planes . History . The Great Door was constructed by two great wizard s , Ostus Agrivar and Parwyyd Hanifar , who worked together to explore the frontiers of magic . They built the Door as a means to easily enter the planes . Each wizard needed the other to control the Door , however , so it remained closed after Ostus ' s death in the Year of the Dragon , 1352 DR . By the Year of the Prince , 1357 DR , the Great Door had been tampered with by an unknown power . It stood ajar and monsters from other planes would later pour from it . Some people grew understandably rather angry about this , and believed that killing Parwyyd would cause the Door to close again . With a small military force , they laid siege to Parwyyd ' s tower , and he considered them " misinformed " . To deal with the Door , Parwyyd lured Kyriani Agrivar to the site . She was the " blood of Agrivar " — Ostus ' s daughter — and bore his magic aura , so she could take Ostus ' s place in controlling the Door . However , one of the faces on the Door spoke , taunting Parwyyd that he no longer had control , and flying kenku s emerged . In the fight , Onyx the Invincible briefly fell through the Door , and saw what looked to be the Hells . Dunstanny — Parwyyd ' s personal assistant — explained that Parwyyd and Kyriani needed to work together close the Door , but as they debated it shot a bolt of magic that separated the merged being Kyriani into Cybriana and Kilili . The power that had tampered with the Great Door then seized greater control , raising it into the air and untethering the interdimensional wormhole from the Door , having it appear in the skies over Waterdeep instead . Kenkus and gargoyle s swarmed over the city , and were engaged by Vajra Valmeyjar and Timoth Eyesbright , before the City Guard and Khelben " Blackstaff " Arunsun took over . In the Hells , a gargantuan and monstrous creature , the one who waits , had seen the other side of the Door appear in its realm . It believed it to be a gift from the god Bane , Lord of Tyranny , and slithered toward it . Its attendants , the gargoyles and kenkus , had gone on ahead . The interdimensional wormhole returned to the Great Door , and the kenkus and gargoyles emerged in the pit , followed by a fire elemental , while the branches of a nearby tree turned to serpents . Cybriana , Onyx , Parwyyd and Dunstanny battled the kenkus and gargoyles until Kyriani was ultimately restored . Working together , Parwyyd and Kyriani first let the door open wide to let the one who waits through , then used " telekinesis " to slam it shut on its trunk , slaying the monstrosity . Parwyyd then destroyed his Great Door with a " disintegrate " spell , and the threat it posed was ended .