On my final morning in Cornwall, the sea is raging. We walk along the beach and decide there’s nowhere safe. We walk to the further bay, and again decide it’s too rough. But out in the harbour in the shelter of the long arm, the waves rock but they don’t thunder. Determined to bid the Cornish sea goodbye in style, we determine to go in right here.

And then Cat spots a seal. Where, where? I ask, panicking I’ll miss him. Right there in front of you, she says and I see him only metres away. He’s huge and shining and whiskered and glorious. And then he disappears and we are suddenly aware of how big he is and how small we are, all in the same water. With the churning motion, we can’t see beneath the surface. I have always, always wanted to swim with a seal and in reality, it’s a little unnerving.

We swim away from where we spotted him, not wanting to crowd him, but he pops up again nearby. I can’t believe it. It seems like a communion with some much more mystical power, some wise abs old and calm and curious being. I hug myself in the water. I never want to get out. But when I start to shiver I do.

From the shore, we watch the seal floating in the waves, popping up, dipping down, unpredictable and strange and wonderful. He stays longer than we can, but only when our shivers get the better of us do we say goodbye.

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