This plunging gorge is the deepest in the southwest, and can be reached via a 1.5-mile rugged riverside hike past a series of bubbling whirlpools (including the fearsome Devil's Cauldron) to the thundering 30m-high White Lady waterfall. Not quite Niagara, but quite an impressive sight nonetheless.
Lydford Gorge
Top choice in Dartmoor National Park