Rising from a seemingly infinite infernal sea of lava in Hell is Demonbane Isle, a monument to the eternal battle between the legions of Hell and the chaotic hordes of the Abyss, and the lair of the Matrons of Malice - Spike, Blister, and Tyke. The structure on top of a black basalt outcropping was fashioned eons ago in the likeness of a balor’s skull from the bones of slaughtered demons and has been bestowed to the coven of midnight hags by the lava sea’s pit fiend overlord, Ba’aldannorr. The coven has been harvesting and trading souls for millennia. They are able to bind the harvested souls kept in soul bags into various forms of items, like weapons, soul gems, magical items, and even phylacteries. Various devils and planar travellers visit Demonbane Isle from time to time to exchange valuable magic items, precious metals, and gems for these custom-made soul-infused items. Such bargains are hard to accomplish with the Matrons of Malice and are always made worse by their unexpected or exorbitant demands that will surely make the customer suffer greatly for whatever they desire.
The Matrons of Malice regard this place as their home, and they regroup at Demonbane Isle whenever needed. The hag coven stores their most valuable possessions in this structure of demonic bone, which they have secured with the most powerful defenses.
The air around the building is blazing from the heat of the sea of lava that surrounds it. The Admission Gate faces the mouth of a giant skull made out of bones fused together perfectly. Within the mouth is the only entrance inside, a large gate fashioned out of dark metal. The areas inside the building are hot but at a bearable temperature and are extremely dirty, messy, and have a foul smell.
Doors and Double Doors. The massive blocks of dark metal that make up the doors were all enchanted by the midnight hag coven. They have AC 20, 60 hit points, a damage threshold of 15, they have damage resistance against bludgeoning, slashing, and piercing damage, and damage immunity against fire, poison, and psychic damage. They open only to the Matrons of Malice and can only be forced open with a successful DC 30 Strength (Athletics) skill check.
Private Sanctum. Demonbane Isle is under the permanent effect of a private sanctum spell, blocking planar travel, teleportation, and divination spells to anyone but the Matrons of Malice.
Sea of Lava. The sea of lava surrounding Demonbane Isle is the domain of the demon hunter pit fiend, Ba’aldannorr, who allowed the hags to create a permanent base at Demonbane Isle. It is considered difficult terrain. A creature that touches or reaches into the lava takes 22 (4d10) fire damage, and a creature at least half-submerged in the lava takes 99 (18d10) fire damage at the start of each of its turns. Completely submerged creatures are subject to suffocation.