Rather than using a service station, I break my journey north from Cornwall with a swim. The wonderful lido guide leads me to Clevedon Marine Lake, a huge expanse of saltwater with an infinity pool’s openness. There are people red with blood-beneath-the-skin cold getting dressed and a man in the distant water. By the steps a couple dangle their feet into the depths. And it is deep and it is distant – the water stretches away, a flat expanse of grey, white, gentle blue, the seaweed encrusted concrete wall marking the only solid line on the horizon.

I go in without a gasp. I swim along by the sea wall with my eyes to the sky ahead, above and settling on the horizon. I pull myself up and look out at the low water of the estuary. The pier in the distance marks an iconic line between land and sea, a multi-arched reminder of humanity’s long standing relationship with these waters. Gulls wobble along the wall, flat footed and squelching, and I let go, sink back, dip my head into the darkness.

I swim to the furthest buoy by the slopes entryway for boats. But there are only swimmers today. Even at mid-afternoon on a weekday, the water is not entirely empty. Though this space is so big and sits on the edge between the everyday abs the wilderness, it is a sense of community I find here. There’s a tiled mural of swimmers in the snow. The handful of people I meet are friendly, chatty. I wish I had a place like this, where I could become a regular but still commune with the wild.

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