Thranconia

Regulus the Binder was a powerful priest of Nodens in the days when the Great Vale was still part of the Realm. He was expert in sealing portals and binding demonic entities. Of the many places he conquered from Evil, the fortress of Quellintan is among the most dangerous. It consists of two levels hollowed out from a large rock outcropping in the plains north of Rathburg and Crossroads Taverns. In this place, Regulus fought a terrible demon-sorcerer of the Herporite race and hurled it back through the basement portal to Hell, sealing it with a powerful spell.

Having cleared the fortress of Evil, Regulus converted it into a garrison to defend the Realm. However, after Regulus went to his reward, the fortress was abandoned and the Vale broken and became counted as among the Wilds. Now, however, the Herporites have begun to rise again. They sent a lesser demon-sorcerer called Fidmul to reopen the hell portal. It began by charming several kobold and goblin chiefs and brought them here to scour the place for the Hell-portal and the means to open it. Fidmul cared not for treasure only for the hellmouth.

In 2019, Mr. Ow and Lothar of the Hill People led a team against Fidmul and his minions, succeeding at last in killing the demon-sorcerer and looting the ruin. However, to the best of anyone's knowledge, the hell-mouth is still sealed up there in Quellintan.

Note: Some references refer to this dungeon as Quasequeton, which is a mistake, that name refers to another famous dungeon complex.