The underground system of Connaught Castle links to Prince's Crossing at several points:
Under the castle itself are several full levels of basements and cellars within the castle foundations. There are several dungeons, storehouses, cisterns, tombs. Several ancient kings had secret personal dens, chapels, studies, and laboratories. Some kept and bred monsters. The system extends down to city cellar level to connect with city points listed above, but most of these tunnels are locked and forgotten.
The system also connects to ancient underground escape routes to Millerton river bank and to Carney Abbey. These tunnels both use ancient “City of Glass” routes.
Connected only by City of Glass, is another ancient underground site, the westwood scarp caverns (also accessible via Skarn Castle ruins.