I was struggling with the height of the walls – 10 metres. I am distinctly medium in height; my two sons tower over me, at six foot, three inches each. But ten metres is a long way into anybody’s domestic sky; and yet that’s how tall the central stone tower of the Broch of Gurness was.

The small cheeseboard (above) bought in Kirkwall, the capital, has served us well as geography prop. Locate the island of Rousay and, from its south coast, drop down to the shark-shaped headland on the West Mainland below. That’s where we are, at the Broch of Gurness, with Rousay opposite, so close you feel you could swim to it – but those waters are treacherous…

I hope someone else is asking, ‘What’s a Broch?’ It’s a well-known word north of the border, but I had to ask the Historic Scotland guide at the tiny visitor…