A city in the Underdark

At some point the small path along the cliff, that you have been walking so far, leads onto a much wider and well treaded one. This path is even laid with bricks, and has other, smaller paths converging on it.

A road? You think to yourself. Why would a proper road be build underground...

Then you see the reason why.

A large underground city comes into view.

It is built out of dimly glowing, blue stone, the type of which you haven't seen anywhere in these caves so far, and it has tall spiraling towers along it's borders, twisting in ways that don't seem achievable with simple craftsmanship.

Was this city built with magic?

You see a hill in the middle of the city, with a long and wide stairway leading up to a gigantic citadel on top.

You can't decide if it looks more like a castle or like a temple.

Around the hill are several large buildings, though none of the come close in size to the citadel. They also look like a cross between the manors of a ruling class and temples. A theocracy perhaps, you ponder. Would these buffoons seriously follow the commands of priests?