Palace of the Shadow King
A gothic black castle, mirror to the Cathedral of the Two-Headed Basilisks in Galgenbeck. Rises over Graven-Tosk like rage rising over pain. Most of the palace lies in crumbling ruins, home to unfortunate souls sheltering beneath its broken halls. None dare dream what might lie under the rubble-covered catacombs and cellars. Tunnels sprawl beneath like writhing roots, digging deeper into the cold earth like cancerous veins.
The inner wing still stands, acting as the home of the Shadow King, a being obscured by ritual. The slaves of the servants of the courtiers of the King come forth and do his will. The title is hereditary: sons are always born to the Shadow King. It's whispered Princes of that line disguise themselves as ordinary men wandering the ruins, engaging in games and tricking travelers, multiplying the miseries of their people.
The Shadow King's lost heir Aldon is imprisoned in the Accursed Den (see Rotblack Sludge). Without him the throne would pass to the Shadow King's imbecile brother.
Graven-Tosk, Shadow King, Aldon, Accursed Den, Rotblack Sludge, Cathedral of the Two-Headed Basilisks
The Shadow King himself is never described physically. The "courtiers" and their "slaves of slaves" structure is suggestive — possibly a hierarchy of bound entities. The under-rubble catacombs are explicitly undescribed as a deliberate horror. The Princes-as-tricksters legend is one entry into the palace; no canonical adventure uses it.