The hill in question is an old hill fort dating from the time of the Dark Emperor. It was of moderate importance in those days, but was besieged during the final war in the final months of the war in -212... roughly a thousand years ago. During the siege, when the surface structures were badly damaged by catapults, the defenders burrowed into the ground, digging extensive tunnels to continue the fight. Once they reached the vast network of caverns that run beneath the Farspar Mountains, they were able to resupply. The defenders were ordered to simply hold out, bleeding off the strength of the allied army. This battle helped prolong the war, but the outcome was inevitable. Powerful curses were laid by the final defenders. As a result the besiegers withdrew shortly after their final assault, and never bothered to clear the tunnels. The surface structures were razed and bodies were buried, but the tunnel network remained largely as it was. Over the centuries, the promontory and ruins have attracted a variety of occupants. Human bandits, goblin bands, orcish tribes, even wandering Sevastin nomads have settled here. All added to the tunnels, and a few attempted to build new fortifications where the old ones stood. None of these communities remained more than a few years before they either departed or disappeared. In the present day, the Keller state of Pine March claims the region. The locals know little of the history of the ruins, other than that it has a bad reputation, and was the site of a battle. The meadows below the ruins are occasionally used as grazing grounds by herdsmen, and the local population of Sevastin periodically camps here, but nobody has settled on the mound in a hundred years or more.
The ruins are a roughly three level promontory, each one being roughly 20-30 feet above the larger one below it. Stone ruins can be found on all three levels. The cliffs are rocky and sloped such that they are climbable, but only just. The risk of loose rocks makes this inadvisable, except at a few points where a loose ramp exists. There are four primary shafts visible on the three levels, each one leading down ten to twenty feet, with a rock stairway along the sides. Each one is choked with debris, plant matter, and bones (human and otherwise). These bones come from bodies tossed in the shafts as middens, as well as from zombies and ghouls attracted by the castle's call. On a 3-4 (3d), there will be a single zombie lying inert in the rubbish at the bottom of each shaft. It will rise up and attack any living humans that attempt to enter the tunnel. Original Basement Levels - Regular rectangular rooms and wide hallways, originally used for storage and dungeons, now choked with debris and dirt. Largely empty except for bats, vermin, and trace evidence of some visiting giant spiders. Each tier of the fort has similar structures that served as quarters for the Dark Emperor's inhuman minions, many of which were vulnerable to sunlight. These basements are basically like the main keep but smaller in scale, and lacking the stairs to the temple. Irregular tunnels spread out from the stairwell going down, leading to...
Siegework Additions - Dug during the actual siege a millennium ago after the surface structures were damaged by fire and catapults, these tunnels included quarters for defending troops, storage areas, guard rooms, and the odd tunnel dug out to intercept a mining attempt. Most of these areas have collapsed, or remain in a fragile state. They have a rough, unfinished quality befitting the circumstances they were dug it. Sections of the tunnels have large guardrooms and traps, places that vicious fighting occurred. A number of giant spiders have made part of these tunnels into a lair. Intruders will be viciously attacked, especially if the spiders are accidentally cornered. The spider lair actually has a few bits of useful treasure on the still twitching corpses of human victims, though the majority of the desiccated corpses are goblins. The spiders generally hunt the woods beyond the hill fort, but have learned to avoid parties of humans, and have a fear of fire and arrows.
Postwar Additions - Goblin warrens, mostly. These look like VietCong tunnels, are usually smaller and open up into larger natural chambers. The key difference between these and the older tunnels is that they are much newer, and consequently much more stable. The small tribe of goblins has set a number of snares in place, as well as things like deadfalls and dart traps. These are both for hunting various tunnel vermin for food, and to discourage intrusion by the occasional troop of Orcs that blunder into the hill fort tunnels while traveling the mountains. There are about fifteen adult goblins and twenty young, armed mostly with small bows and javelins. They survive but hunting at night, raiding local farms, and with fungus farms in their caves. They are cunning but cowardly, and will generally only attack humans at night, from ambush. They rightfully fear predation by both spiders and the bugbears, but every full moon they make a ritual of bringing a sacrifice to the temple, whether human, orc, or one of their own.