About eight miles north of Tavistock, Lydford Gorge is the deepest river gorge in the south-west: the River Lyd has carved a narrow chasm through Dartmoor's granite, and a National Trust path runs along its length. The dramatic point is the Devil's Cauldron, a swirling whirlpool reached down a steep iron staircase clamped to the rock; at the other end of the walk, the White Lady waterfall drops a hundred feet through ferns and moss.
The full loop takes about three hours over uneven, sometimes slippery paths — sensible shoes are needed and not advised in heavy rain. The village of Lydford above is worth a stop: the ruined Norman castle was once Dartmoor's stannary prison, notorious enough to enter the Devonian phrase "Lydford Law". The Castle Inn next door is a good lunch stop.