The hollow sound you make crossing a wooden bridge.

These wooden spans used to scare me as I looked over the edge at the rocky depths.  The wooden planks seem so flimsy, what with gravity and all urgently calling your name.  And in the movies these things ALWAYS break and drop dozens of unfortunates into the gorge below, their cries cut short by distance and churn.  But once you overcome your clearly overactive imagination, the hollow sound of your steps is a harbinger of security; of safe passage over the yawning air.