Undercity

The Undercity or Eldercity was a ruined, underground city under Baldur's Gate, the remains of an older city that once stood there. It could be accessed through a trap-filled, monster-ridden maze beneath the city's thieves' guild. Located in a vast cavern, the Undercity consisted mostly of broken-down shells of buildings haunted by undead. The one building that still stood was a temple to Bhaal that was used by Sarevok as a secret lair where he was supposed to perform the rituals to ascend to godhood. Instead, it came to be the site of his final stand against his half-sibling after his plans had been foiled.