As mentioned in my first d23 post, the entrance to the dungeon leads to the lower works of Castle Silverlion. The Castle has been a vague notion I've had for a while, as Gygax exhorts (or mayhaps implores?) the DM in the DMG Appendix A to generate the upper works above the dungeon, something he often didn't do and which his successors have largely abandoned.
Castle Silverlion is the former ancestral abode of the Silverlion family, petty nobility whom claim varying authority and rights from the Free City of Silverlion. It stands on a hill overlooking the city.
The Upper Works have fallen into ruin and rot one is hard-pressed to argue have any natural cause, overgrown with moss and often strangely fog-choked even on clear days. There is no real treasure here, and despite some overgrown vermin, the main threat is some groups of greedy villagers, bandits, and/or brigands waiting to jump exiting adventurers.
The Lower Works are in much better shape than above, and there are more vermin and less knaves. It is also long-since looted and quite mundane, with typical storage, bunk, and gaol/jail rooms. Toward the far north end is trap door, a mighty square of black iron the feels cool on hot days and warm on cold days, with two handle-rings. It requires a combined strength of 20 to lift up fully from above or push up from below and leads to room 1 of the dungeon.
There is another entrance, a shaft on the hill below the Castle called "Matilde's Folly" that leads to a lower level (3?) and at least one other rumored secret entrance.
Brief history of Castle Silverlion and Silverlion Family
~250 years ago: Henri Elf-blood is created Lord of the Manor by King Njall III for his service on the borderlands. He adopts a silver lion passant on a blue field as his coat of arms, and a town of uncertain name is rechristened "Silverlion's Town"
~230 years ago: Castle Silverlion's Upper and Lower Works are completed and remain largely unchanged for almost a century.
~180 years ago: Rivalry between brothers sees Claude Silverlion abandon the Castle and town (by now simply called "Silverlion"), leaving his brother Pierre Silverlion as the unquestioned authority of the locale
~130 years ago: Sole heir Luc Silverlion answers the call by many churches for a Lawful crusade into the Chaotic realms of the west.
~125 years ago: Luc returns home, his quiet and thoughtful demeanor turned aloof and cold. Pierre, already in bad health, dies a few month later.
~124-120 years ago: Luc becomes withdrawn. Slaves, both human and other, are brought in to perform mysterious labor in the castle. The villagers are worried but otherwise hands off, as Luc requests very little labor from them and channels much of his tax rights back into food and raw materials. Most family servants leave or are dismissed
~119-118 years ago: After two years without sight or sound of Luc or any of his remianing servants, the mayor and other local grandees reach out to Claude's branch of the family.
~117 years ago: Jean-Claude Silverlion, a man of staunch piety and healthy superstition, arrives with his wife and child. He assembles a posse to investigate the abandoned Castle, and upon venturing beneath the black iron trapdoor and seeing the pillars below, tells his men to grab all valuables they can carry and flee to town. He warns the village that there is something Evil beneath the Castle and to avoid it. He and his family relocate to a manor in town.
~100 years ago: The Castle begins to rapidly, and almost supernaturally, fall into disrepair. An unexplainable fog often shrouds it.
~50 years ago: Headstrong and independently wealthy from past expeditions in the borderlands, Matilde Silverlion and various mercenaries begin excavating a shaft on the side of the hill for not-understood reasons. After local miners refused to continue due to strange illness, foreign laborers and slaves were brought in. She and her party spoke of discovering a structure beneath and mounted an expedition but never returned.
