Kostchtchie's Maw

Kostchtchie's Maw, was a massive prison and water-filled chasm found on Avernus, the topmost layer of the Nine Hells. The prison's name derived from the fact it was the one-time prison of Kostchtchie, the demon lord who had been stripped of his favored weapon and shackled within by Zariel.

Description
The infernal prison comprised a chasm, some  wide and  deep, filled with the murky, mind-altering waters of the River Styx. Only a portion of the waters' depth within was visible, however, as what lay beneath was unperceivable from the battleground of Avernus.

Before it became flooded, Kostchtchie's Maw was an enormous pit set within steep cliff walls. While these cliffsides were traversable with some effort, the journey was precarious and fraught with peril. Within its depths was an enormous tar pit, some wide and  deep.

History
Some time during the late 15 century DR, Kostchtchie was freed from imprisonment within the maw that bore his name. The chasm was then repurposed as a prison for the soul of the Storm King Hekaton, who was bound to Toril as an undead servant of Szass Tam.

Notable Locations
Within the bottom of Kostchtchie's Maw was Mirror Maelstrom, a stronghold of black iron that resembled a twisted facsimile of the storm giant fortress of Maelstrom on Toril. Its surface was crusted over with barnacles composed of hardened magma and warded to protect it from divination and teleportation magic.

Inhabitants
When it remained empty, Kostchtchie's Maw held only the demon lord himself, restrained by magical chains that continuously tightened over the demon lord's form. He was guarded by his infernal jailor, the kyton Mazer and his four hell hound minions.

Later on, Mirror Maelstrom housed a myriad of devils that watched over its prisoner, including yugoloths and mortal Red Wizards from the Faerûnian realm of Thay.

Appearances

 * Adventures
 * Baldur's Gate: Descent into Avernus
 * Organized Play & Licensed Adventures
 * Avernus Rising (The Harrowing of Hell)