Thræsh's Hold

Come on, just look at it numbskull! It is damn fortress carved into a mountain. Of course there'll be treasure.

— Keronian, treasure hunter extraordinaire, three days before his alleged suicide.

When you travel to Moondoor, the city at the Mountains feet, you can not really miss it. An ominous fortress towering over the city, far higher up the mountain range than any other building in the city.
The Hold as it is sometimes called by Moondoor residents is an imposing building of black marble, which contrasts strongly against the often snow-covered ranges it is carved into. It towers over the city looking down on the many winding streets and the slowflowing river that cuts the city in two, almost like a disapproving old man observing loud and rowdy children playing beneath his windowsill. Many myths surround the Hold but the most pressing one is of course why it is still standing:

(Almost) as old as time itself

Moondoors westernmost districts are the closests to the mountain itself, where the city walls join directly into the rock of the cliffsides. There building upon building is built into the slope of the mountain, but when you reach a certain height all building stops. No one dares to build closer to the Hold, partly out of fear of the old walls, but also out of practicality. Rockslides are not common here but also not unheard of and the higher up you build the larger your chance one might hit your house.
Then as you ascend the mountain side, for a long while there is no sign of civilisation at all. Finally you reach a plateau just beneath the summit, where the Hold itself stands. The dark parapets and stone interior seems almost like a black void up close and more importantly it shows no sign of decay. Despite being older than any building of the city not a single piece of rubble is to be found and even intentionally trying to damage the fortress seems to do little to nothing at all to it.
The fear of this place by residents of Moondoor is so deeply ingrained that barely anyone even attempts to visit it. On the rare chance that one tries to make the climb they not only need to deal with the nausea inducing stairs, climbing up almost like a ladder in parts, with no railing or any aid whatsoever. No beyond the dangerous climb itself, Thræsh's Hold seems to weep out despair, dismay and fear like black ichor, the feelings permeating the air. If a particularily foolhardy or brave person does make it all the way up the mountain they find.

Emptiness

The fortress is long deserted. Even if there was no mystical aura of emotion surrounding the Hold, it would not be feasible to live here year round, for every bit of food and equipment, least of all firewood to work against the cold, needs to be brought to this elevation under intensive manual labor. No beast of burden can make this trip at all and so everything needs to be carried by hand.
And so, the castle stands empty, its doors still swinging open with ease as if an invisible valet had just oiled the hinges, and not one soul lives up here. Yet, ever so often, Moondoor residens swear on their parents graves that they see a single candle light moving behind the windows of the Hold far up in the mountain, as if the fortress had never been abandoned.

Whats in a name?

Thræsh's Hold gets its name from Lord Thræsh, a mystical figure from the ancient days long ago. If you want to learn more about the myth himself, you can follow in the footsteps of Mary de Suin, a historian who tried to unravel the mystery surround the name-giving figure of the Hold:

If ancient myths are less your wheelhouse, you can also learn more about Moondoor, the city at the foot of the mountain.