A few years ago I took up running. It wasn’t long before I stumbled on the kerb, turned my ankle and had to be scraped off the road by a passing motorist. A physiotherapist subsequently told me that injuries within six weeks of taking up a new activity are commonplace, if not inevitable.

Once I had stopped hobbling I decided I would swim instead. I didn’t much like running anyway, I’ve always loved the water, and swimming has almost zero physical impact. It also refreshes the parts that running doesn’t reach.

These days I swim regularly at the leisure club in what was once the second home of the Dukes of Atholl, to which they decamped for a century or so when their castle became too damp and draughty to live in. More recently it belonged to Hilton until they sold it to a private group, last year.

Most evenings now I try and get over there to swim. The exercise, and the random conversations that take place in either the jacuzzi or sauna afterwards, have become an essential part of my daily winding-down routine. Earlier this week I found myself discussing the relative merits of swimming and the gym with the only other occupant of the sauna.

‘I didn’t learn to swim till I was in my forties,’ he confided. ‘Perhaps you didn’t need to?’ I suggested. He pulled a face. ‘Not much point where I was.’ I asked the obvious question. ‘150 miles west of St Kilda,’ he answered. ‘Rockall.’

‘Rockall, Malin, Hebrides …’ To most people it’s a place described in meteorological terms only, one of the names in that almost mystical litany that is the shipping forecast; an indeterminate expanse of ocean haunted by gales, low visibility, rapidly deepening pressure and many of the other natural phenomena so sonorously forewarned across the airwaves.

In physical manifestation it’s the pinnacle of a submarine mountain, a lone, uninhabited rock that thrusts up from the Atlantic like the snout of a breaching whale. As its name suggests, this most westerly point of the British Isles boasts no living thing but seabirds. Immersion in its icy waters would mean death within minutes.

I know about it because my son-in-law is one of the very few people ever to have landed there. In his more adventurous days he volunteered as a ship’s doctor for Greenpeace. On one voyage he and a shipmate took an inflatable and negotiated the swell to get within scrambling distance of the rock. Once ashore, if that’s the correct term, he collected a small sample of rock which he took home and later used to make a homeopathic remedy. It was for loneliness.

I told my sauna companion this story. He became pensive. ‘I fished out there for twenty years,’ he said. ‘It was only when I stopped that I realised that during all that time my wife never had any idea where I was.’ He didn’t add, ‘Or if I was coming home,’ but it hung unspoken in the heated air.

I asked what he did now. ‘I manage wind farms,’ he replied. ‘The west and north of Scotland, from Campbelltown to Orkney. That’s where I’m from, Orkney.’ I made a  comment about the contrast with fishing. He smiled. ‘I do a lot of talks to schools these days. I tell the children that I used to harvest fish. Now I harvest the wind.’

I asked him if he still missed being at sea. He nodded slowly and gazed through the glass door of the sauna to the pool and the gym beyond. ‘I’ve recently taken up ballroom dancing,’ he said. ‘I love it. It’s hard work, mind. But it’s brilliant. And the lassie I’m partnered with – turns out she’s from Orkney too.’

The threads of our lives weave portraits that only others can see. Sometimes there is something in the weft that catches the eye of the bystander and holds it for a while. Several days later I continue to think about the non-swimming, wind-harvesting, ballroom-dancing, Orcadian former fisherman and his life.