Castle Stalker is a medieval granite miracle on an island on Loch Linnhe, 25 miles north of Oban, and a ravishing treat even in the Highlands, a region brimming with them. It has few visitors, not least because owner Alasdair Allward has to ferry them across in a small boat. Clans batted the castle between them, each change of hands marked usually by a murder, until it fell into ruin in the nineteenth century when the owners bought a much less drafty Georgian house.

The affable Alastair’s father Stewart purchased Stalker in the early sixties. It had no roof and no floors, but it did have 9 foot thick walls.  Stewart and his family restored the castle more or less as a labour of love. A soldier and a lawyer, Stewart was a devout Scot who lived in Surrey. The family law firm had a long list of clients in various trades who were invited up to Stalker for holidays and asked at the last minute to bring their tools . . . Alastair, the only son of four, was picked up from boarding school at the end of each term and driven to the castle, where he spent the entire holiday mixing concrete by hand, assisted by his mother. One year, Stewart gave his wife a concrete mixer wrapped in a red ribbon for her birthday. It remains a home, a delightful blend of thirteenth-century stonework and 1970s MFI furniture.

The team had to float the biggest beam over, to go above the fireplace in the drawing room, but it sank, and had to be dragged. The roof beams, made of Canadian hemlock, had to be pushed up the hill on rollers. The dungeon, under the great hall, is now covered with glass tile under a wooden lid. Six from the losing side at Culloden met their end there.

You can book Alasdair’s two-hour tour online or by phone; he leads about five tours a week in season, taking 14 people over at a time, and it costs £20 per adult including the boat trip. Also, catch up on YouTube with the scene in Monty Python and the Holy Grail in which the castle appears – with the 20-year Alasdair playing a rude French knight when two Pythons approach in a Viking longship asking after the Grail. (He’s is the one putting his thumbs to his forehead, waggling his fingers and putting his tongue out.) He says it was, ‘The funniest day I ever had’. The Viking ship was made in half a day by the crew from an old rowboat, mocking up the elaborate prow and draping it with seaweed. The film was made on a shoestring, using hitchhikers for extras and paying their £50 Stalker location fee very late.