The jubilee pool in Penzance has been somewhere I’ve longed to swim since I first saw photos of it years ago. So being in Cornwall and just a short drive away, we make it the centre-piece of a three swim adventure day. It’s very different from the wind-lashes beaches and dicky vibes we’ve been wallowing in recently – not merely because here I feel I need to make an effort to do at least a bit of proper swimming. And it’s nice – it’s nice to stretch out over flat, dark water, to cover distance, to feel the forward propulsion of limbs without the backwards push of waves. It’s nice because I have been revelling one the wildness and the challenge of the water and here it is different and here I can actually swim.

The saltwater is silky and dark and below the surface is mostly sodden green. It holds you up and makes your glides last forever, makes your skin tingle in the sun and open eyes sting. It’s deep and triangular and so bridges the wild and the manmade – calm like a pool, but salty like the sea. The shape encourages meandering, swirling swim paths or – at the very least – makes a change from the normal one up, one down boxes we are used to.

The sea is just over the wall and you can hear the waves. The paint on the sun steps is peeling and thick with outside air. Afterwards we eat in the cafe looking out over the jewel blue of the pool and feel grateful that generations ago, people loved swimming enough to build this place.

I’m raising money for the Alzheimer’s Society. Please sponsor me at http://www.justgiving.com/swimbonnieswim