Dunn's River Falls is the defining experience of Jamaica's north coast — a terraced limestone waterfall that cascades 180 metres from the mountains down to the beach at Ocho Rios, with visitors invited to climb every step of it. The climb is done in human chains, with each person holding hands with the next while a guide leads the group upward over slippery rocks and through pools of rushing water. It sounds more alarming than it is; most visitors manage it, and getting soaked is part of the deal.
The falls are undeniably beautiful, and the experience is memorable, but go in with clear expectations: this is a major commercial attraction, and the crowds can be formidable when cruise ships are in port. Go early in the morning for the smallest crowds, bring water shoes if you have them (they can be rented on site), and ignore the vendors at the entrance. If you're here midweek without a cruise ship in port, the experience is considerably more pleasant.