The Temple of Logarth
Background
Many many years ago, a temple was built in the forest of Boreum, an uncivilized forest located near a coast along a trade route, very far from any cities or towns. The temple was dedicated to a god of evil (whichever suits your campaign) and the priests there conducted terrible sacrifices and constantly attacked any ship that passed near the coastline. Several years later, some stray adventurers discovered the temple and somehow managed to escape and inform the nearest city, the king of the land sent several army units to lay waste to the temple, and after a furious battle, they managed to defeat the cultists and slay them all.
The temple was in ruins, and the local inhabitants (primitive tribes of elves and humans) avoided it completely, believing it was full of evil spirits, claiming that anyone who entered the ruins never came back. The only creatures that dared enter the ruined temple was a tribe of hobgoblins, claiming that they had reached a pact with a dark god that resided there.
About a year ago, some runaway brigands came to hide in the forest, and had the bad fortune to run into one of the human tribes, starving, the brigands attacked the village expecting an easy victory over the primitive warriors, but it was not so, the tribe's numbers and knowledge of the forest allowed them to defeat the brigands, leaving few survivors. Those who lived (including the leader and his lieutenant) fled deeper into the woods, hunted by the tribesmen.
After several days, the surviving brigands came to the temple and hid in there, the tribesmen, aware of the legends of the place, ran away.
The lieutenant, with the help of a wand of metal and mineral detection, discovered a great amount of gold within the ruins , and so the brigands decided to explore them, only to be captured by the hobgoblins and presented to Logarth, their "god" (a gauth, beholder kin). Many of the brigands were killed, but somehow, the second in command (Nayal) managed to strike a deal with Logarth, promising magic offerings. Soon after that, Nayal discovered that there was a gold mine in the mountain upon which the temple was carved, and started to exploit it, using the hobgoblings and slaves captured from the tribes.
Soon after, Nayal thought it would a good idea to exploit the tribes superstition, and so named himself the high priest of Logarth, the all seeing eye.
What is really going on
The so called "dark god" is nothing but a gauth (a beholder kin that feeds on magic items, see MM, page 21) that took residence in the temple a while back, hoping the temple's reputation would attract mercenaries or adventurers loaded with magical treasure.
Several years later, a diminished tribe of hobgoblins came to the temple, seeking refuge, Logarth appeared before them, and the primitive creatures believed him to be a god sent to help them, the gauth saw an opportunity in this, and told them he would help them as long as they brought him magical offerings.
When Nayal arrived, he convinced Logarth he could get him power and magic to satisfy him for a long time, telling him he had found gold within his ruins, Logarth allowed him to live and to carry out his plan to appear as a high priest, knowing that the tribes would fear him even more.
Since then, Nayal and his new associate have exploited the mine using slaves from the tribes caught by the hobgoblins, and have used that same gold to hire numerous brigands to tax the tribes and enforce their will. At the time the adventurers arrive, Nayal has a small army at his disposal, with strong forces camping near the villages of the region to keep them in check, and the temple is protected by the hobgoblins and a numerous groups of brigands, including some wizards who pose as clerics of Logarth.
With this forces, Nayal has sacked the villages and taken many warriors as slaves (with the help of Logarth's feeblemind spell effect) and is working the slaves to death, hoping to muster enough mercenaries to attack the civilized cities to the west.
Adventure Hooks
The tribes
There are six tribes in the region, four human tribes and two tribes of elves, they will be willing to cooperate in anything, including assaulting the encampments (but the tribes are very weakened by the last raid). But under no circumstance will they go near the temple, they believe it to be haunted and are too afraid to go, and they have colorful rumors about it (the high priest flies above the mountains at night, carried by spirits. Logarth can kill a man just by looking at him, hmmm... well, not exactly a rumor. The priests have summoned demons to guard the temple. The hobgoblins have turned into gargantuan beasts, etc.).
The tribes are not aware of Logarth's true nature, and refer to him as "the all seeing eye" or "the dark god".
The Temple and its inhabitants
The now called temple of Logarth is a magnificent estructure, carved on the side of a mountain and made of white stone, from outside, the temple looks like a tall white tower and can be seen from miles around. The mountain upon which it is carved is very dangerous and difficult to climb, making an attack from above nearly impossible.
The temple has only four floors (although it looks much taller) and most of the estructure is carved inside the mountain. The first floor is reserved for receiving goods and bounty from the tribes, the second has the barracks, the third is reserved for the high ranking cultists and guests, and the fourth contains the great altar, Nayal's room and Logarth's lair. Deeper into the mountain, tunnels have been excavated to extract the gold.
The hobgoblins are the only ones that know of the gold mine and Logarth's true nature, and fight as fanatics.
The brigands and their leader (Grax, a tall, strong warrior, F8) do not know about the mine, and are not sure if Logarth exists or not, and many believe Nayal to be the leader, all they know is that something is going on at nights in the area reserved for the hobgoblins, and that something powerful is at work.
There are four dwarf engineers staying on the third floor, they were brought here to make sure the mine doesn't fall apart.
Eight ogres reside in the temple, sometimes patrolling the woods in search of strangers.
There are four sword spiders in the temple, reserved for torture and for making examples of rebels.
The druid of the forest and other villagers are held in the dungeon, starving and agonizing, they are not strong enough to work in the mine.
Four wizards (level five or six), posing at clerics, also live in the temple, they, like the brigands, are not aware of the gold mine and Logarth's nature.
Nayal, a half-elf fighter/wizard (6/6), he is very intelligent and cunning, taking advantage of everything and everyone, but contrary to what Logarth thinks, Nayal is terrified of the Gauth, and has no plans of betrayal whatsoever, he considers him a very valuable ally.
Logarth, the gauth, for his part, is quite pleased with the recent developments, he has no interest in gold, but he has been well fed by Nayal. But he thinks that the half-elf is growing a little too ambitious for comfort, and is considering replacing him.