Description taken from RCPedia.

Set into the street of Ferret and 10th, there is a trapdoor. If one possesses the key to this door, and has the inclination to explore, they will find a narrow spiral staircase leading down into the murky depths of a shadowy crypt. A network of slave-dug tunnels extends from this crypt to Elm and 1st, the domicile of his sire Sartori, and to Aardvark and 1st, the family estate. A tunnel also extends into the cellar of nearby Balmer's Tavern.

Burned into the wood of the trapdoor itself is the coat of arms of the D'dary line.

Links to destinations of tunnels as per description: Balmer's Tavern, ...