Im from Holland, so please pardon my English:)
A long time ago i heared somebody ask me about the Stoneheim mystery. You know, about the dwarves collapsing the barbican?!
Now, it is clear that there must be something important there to protect. As you look at the Dwarven nature to carve rock and mining, it is, as alot of you agree, fair to say that Stoneheim is carved out of the mountains.So, its possible that a even larger city exists underground, extending under the mountains surrounding Stoneheim and Myrghard. With Tunnels going all the way to.. lets say, Covenant.
Take the dwarven city of Moria from Tolkien's "Lord of the Rings" as an example. A huge complex, carved out of the rocky earth. A great place to keep your tressures, dont you think?