This triangular art deco lido was built in 1935 to commemorate King George V’s silver jubilee and has stunning views over the Cornish coast. The main lido – the largest seawater pool in the UK – is unheated for an ‘authentic’ (read: quite chilly) sea swimming experience. But it recently also became the first in the UK to use geothermal technology, with one section of water heated to a toasty 35C via a well dug 410 metres below the earth.
And if that isn’t sustainable enough for you, the lovely café is plastic-free and uses only seasonal, locally sourced ingredients. They even recycle broken pool inflatables via a specialist charity.