I had an idea of a map with something that could be used for more investigative adventure. Instead of abandoned ruins and murky dungeons, I decided to go with a temple that is actually a façade for a demon, an immortal monster or an undead monstrosity, like a vampire. I didn't want to specify what the monster is, so you can pick your own favorite monster of the week that fits the PC's power level.
A days travel away from the City, there is a peaceful valley surrounded by mountains and large hills. At the bottom of the valley there is a lake and on the lake's shore there is small town of Lilyvale.
The town is known for its excellent salmon and beautifully embroidered clothes the townsfolk sell in the City. A bit further, on the northern shores of the lake, there is an old temple.
The temple is built on the cliffside of a small mountain next to a river flowing down from the mountains. There is a rickety suspension bridge over the river leading to the temple's entrance. The suspension bridge cannot stand the weight of heavy beasts of burden or horses. A small donkey or mule might be able to cross the bridge, barely.
The temple seems ancient. There is moss and vines growing everywhere, floor tiles are cracked in many places and the doors creak as they are opened and closed. Engravings on the walls are written in languages long forgotten now and depict events from ancient mythologies only few know anymore.
The priests of the temple, call themselves as the servants of Aelmatar, the patron of life and death, and for gold or a worthy sacrifice they will heal the ill and take care of the dying. The priests are dressed in brown robes with red veils covering their faces and white ropes as their belts. Most of the priests wear ritual daggers on their belts and a few of the priests assigned for guard duty wear ornamental shields, silver-edged sabers and short bows. The guards wear a light leather armor under their robes.
Usually there are a few patients being treated. Either healing from their wounds or illnesses, or being cared for before dying of old age. For a generous payment the priests are willing to perform a secret ritual that will heal almost any mundane illness or disease, or even resurrect the dead. Provided their body is intact and preserved.
People who undergo the ritual are cured of all ailments and diseases and brought back to life scarless and with no signs of any injury. But there is something wrong with them. If they ever leave the temple, they feel drawn to it as long as the Master is alive.
The Order of the Nahkhiir
Nahkhiir, the Deceiver of Life and Death, in an ancient deity worshipped by few. Nahkhiir is usually presented as a bat-like creature with humanoid features. It is told that Nahkhiir is the bastard child of the gods of life and death. The servants of Nahkhiir are secretive and often present themselves as monks or priests of another religion. The children of Nahkhiir, as the servants are also known, do not see any conflict in this, as Nahkhiir is the great deceiver and pretender.
The servants of the Nahkhiir sacrifice animals and precious spices in their rituals, but the greatest sacrifices are lives of humans and demihumans. Most treasured of all sacrifices is the blood of elves.
Hidden doors inside the temple lead into the dark and damp caverns inside the mountain. The caverns lead into ritual chambers and the den of the Master.
The Master is an immortal creature feeding on the life-force of the living, but it also has the power to heal and resurrect from the dead by giving its own foul fluids to the ailing or dead. Consuming the Masters nectar will restore a person to full health and even increase their vitality for a month, but it will also create a telepathic bond with the Master.
The Master can sense anything the person sees, hears or feels. After a month the person will create an irresistible draw back to the Master and will start losing health until they get more the Master’s nectar. If the Master is destroyed, all the side effects of the nectar will vanish.
The Masters den has a foul stench and is littered with decayed corpses of past sacrifices.
In the Master's den there is a pool of murky water where all the valuable possessions of the sacrifices are thrown into. The pool is quite deep, but a capable diver can retrieve a significant treasure from the pool. There are even a few magical items in the midst of all the coins and jewelry.