Hampstead bathing ponds

The lowdown

Three spring-fed ponds sit up on Hampstead Heath: one for men, one for women, one mixed. People have swum in them for over a century and they are still one of the only proper wild swims you can reach on the tube.

There is no chlorine and no clock. Just cold water, ducks for company and the city somewhere behind the trees. The lifeguards are there year-round and the regulars will happily tell you the water is colder than it looks.

It runs on an honesty box. A fiver gets you in, less if you are concession, and nobody is checking. Bring a towel, flip flops and the kind of confidence that survives a 6am dip in November.