Schluesselschloss
It guards the bottle-neck at the Reikland-end the Grey Lady Pass, and is situated on an Island in the River Schlusselschosselschlucht (or something..). Unbeknownst to it current occupants, this rocky island is the Tomb of a long dead Hero of the Empire named Otto (someone or rather), who has been sealed in a cave with Holy Wards on account of being turned into a Vampire in his final fight centuries ago. Thus it is a literal 'Lock', hence the name, but the true meaning behind it has been lost over the centuries.
Otto has a Palantir-like artifact called Black Orb which lets him manipulate bearers of the other Orbs, including the Steward of the Castle above him, a Goblin Shaman who has the ear of a dangerous Warboss (figuratively), and a Night Goblin in the tunnels below. He uses his influence to manufacture a siege of the castle in the hopes of freeing himself.
The castle itself is being mis-managed by the Steward, and so its defences are a shambles (cannons are in disrepair, standing army are complacent and over-fed).
