On the Eyes of Midnight
Monastery of the Lost
Once a home to Markovian Monks, this monastery was overcome with an infestation of devils after some of the monks had begun dabbling in Asmodian tomes hidden within its lower levels. The monastery and all its keepers were overrun and most were slain by the demonic hordes. However the stronger were turned into cultists of Asmodeus through means of blood magic and forced tutelage.
Malevolancy this powerful stood out like a beacon in the night to the various lords of the demi-plane. They sent armies of the night in attempts to squelch any force that would rival their own. However, after many failed attempts the dark lords including Strahd himself resorted to even more extreme measures.
It is said that the dread plane and its controlling lords purposely fell silent and allowed the small points of light and good throughout the realm to band together and snuff out this evil. The high priests of Pelor and its stalwart warriors, joined by various others from an amalgam of faiths led an assault on the monastery. People rose up for the first time in centuries, and crushed the demons within the monastery, forcing them back into the underworld and bringing a renewed hope to the demi-plane. All of this without interference from the dark lords.
The dark lords of the realm allowed its citizens a brief period of renewed hope and prosperity, only to wait for the exact right moment to realign themselves as the most powerful and fearsome force within the dread plane. Desecrating their temples, killing innocents in plain sight, amidst other ghastly displays of power. Clergymen were burned at the stake and all who sought to do good within the lands. The dread lords had returned.
And so the realm descended back into darkness, the monastery untouched for centuries.