The Changkong Zhandao — "Vast Sky Plank Walk" — is the most famous and most terrifying section of the Hua Shan trail system. It consists of narrow wooden planks attached to metal pegs hammered into the near-vertical southern face of the South Peak, with iron chains to hold as you sidle along a ledge barely wide enough for your feet. The walk accesses a meditation cave that sits in the cliff face below the summit.
You are issued a safety harness at the start and must clip in to the chain. This does not prevent many people from freezing in place. The walk is not particularly long — perhaps a hundred metres — but the exposure is extreme, with nothing below you for several hundred metres on both sides and above. It is popular specifically because it is terrifying: on weekends, queues form. The actual cave at the end is pleasant and quiet, and the view back along the plank walk from inside it is the best photograph you can take at Hua Shan.