Make a city setpiece
Mountain Greatbridge Ruins:
Visible from any point in the city is the towering support of a colossal bridge that once spanned the nearby valley and connected two mountaintops. There is a matching one on the other side of its span, and several fragments of its deck can be found in the valley below. It is made of a material unlike those common to the region, colored a deep blue-gray and unusually heavy. Both the supports and fragments of the bridge are adorned with geometric patterns reminiscent of but not identical to ancient architecture that can be found in the city's nearly-forgotten catacombs. When viewing the bridge support during a nighttime storm, it's said that a a faint blue glow can be seen coming from the patterns.
Nobody knows who built it or why, and the collapsed bridge has stood in its current state as long as anyone can remember. There are some rumors that the city of today was built atop the ruins of a previous civilization, also responsible for the catacombs. Those people, whoever they were, abandoned this region long ago.