The Ancient Bridge

From the introduction: For a person afraid of heights, one of the more daunting things to face is the prospect of being suspended above a large height by something that may or may not be able to support you. Add to this the idea of something actively trying to send you falling into thin air and you have what an acrophobic might consider to be their worst nightmare. Tell your PC’s to hang on to something for this encounter, lest they plummet to their deaths.