Twilight of the Gods
Dvergar delvings differ from the realms of the alfar and the huldufolk in that they are not usually magically hidden. Delvings are well-defended by dvergar warriors, as well as cunningly-built traps, false doors, murder-holes and dead-end caverns.
Grava Delving is just one such. The visible entrance is a stone door, and only the dvergar can open it.