Some people call it crazy: Gorge walking, known as canyoneering in the U.S., means following the course of a young river, going where the water goes. If you encounter a waterfall with a deep enough pool below, you jump! In Brecon Beacons National Park, you can crawl, run, jump and swim along the fast, boisterous water, sometimes getting immersed in it, sometimes resting in deep, deep quiet. Along the way, though, you'll be discovering the best little spots in the hills.

Farther west you'll find a variation on the theme—coasteering. You climb down a cliff, sometimes scrambling, sometimes rappelling, to the sea below. Then you swim across the bay and climb up the cliff out on the other side. Rough weather only increases the excitement.