There isn't a dwarf alive who remembers the Deep Roads as they once were. They were the network of tunnels that joined the thaigs together. To be honest, it isn't even right to give them such a simple term as "tunnels": They are works of art, with centuries of planning demonstrated in the geometry of their walls, with the statues of the Paragons that watch over travelers, with the flow of lava that keeps the Deep Roads lit and warm. The cloudgazers up on the surface talk of the Imperial Highway built by the magisters of old, a raised walkway that crossed thousands of miles, something that could only have been built by magic. Perhaps it is comparable to the Deep Roads, although we dwarves didn't need magic.
I suppose it doesn't matter any more. The darkspawn rule the Deep Roads now. When Orzammar sealed off the entrances to the Deep Roads, abandoning everything that lay out there, we handed over the kingdom-that-was to those black bastards forever. To think that there are genlocks crawling over Bownammar now, tearing down our statues and defiling our greatest works! Corruption covers everything we built out there. Every dwarf who goes out and comes back says that it gets worse with each passing year, the foulness spread a little further.
And the cloudgazers think the darkspawn are gone just because they aren't spilling out onto the surface? Huh. One day, when Orzammar is gone for good, they'll find out differently. Those darkspawn won't have anywhere else to go but up, and they'll do it. The surface folk will have themselves a Blight that will never end.