Mousehole Tidal Pool, Cornwall, UK. Until the 1950s and the rise of the heated indoor swimming pool, children learnt to swim outdoors. For those close to the sea, many man-made tidal swimming pools were constructed around Britain’s coastline. Heated by the sun, these tidal pools were often built to keep bathers safe from high and rough seas, which explains why so many of them are clustered in Scotland and around the surfing beaches of Cornwall. Whether they are simple swimming holes made by shoring up natural rock pools or grand lido-like pools complete with lifeguards and tea huts, they are all refreshed by good high tides.