The Great Expanse

The 50ft wide bridge spans a gap countless as many times as long. Who built this bridge in the middle dark to span this gap? Are they watching us right now? The bridge is immaculately maintained, but is it simply magic or something more sinister? It was in fact built by the magic of a long lost wizard, and maintains itself through the creatures that live beneath the bridge. They are trolls because the wizard thought it most ironic to do, and they keep the area lit to attract things from throughout the Underdark as well as to allow them to see what is happening. The trolls have set up living areas beneath the bridge, and do well to gauge the power of those that are crossing and leave well enough alone when the odds aren't quite in their favor. Their population is culled because they get too ambitious from time to time when their numbers are too great. - Joatmoniac