IT takes a while for us to get in. There are only so many times you can say you don’t want to join the National Trust. A bit too costly. Too many places to visit. All those shops selling tasteful stuff you don’t really need, even if you think you might. All that jam, for heaven’s sake.

Not that we say any of this, being too politely English.

Castle Drogo isn’t a castle and has nothing much to do with Drogo. The owner, Julius Drewe, just fancied they were related, so chose the name. Described as the last castle to be built in England, it has seen no battles, apart from the one that raged between Drewe and the architect, Sir Edwin Lutyens, over the leaky roof.

Drewe was a retail tycoon who was so successful he retired at the age of 31. In his back pocket he had £60,000 to build his splendid folly, a copy of a Norman castle with Tudor touches and modernist additions. His sixty grand would be about £20 million today. Much of that money he made importing tea, the rest from founding the Home and Colonial Stores.

The roof leaked from the start. Drewe and Lutyens stormed about the place shouting at each other, and the only reason that Kevin McCloud wasn’t there to film it all was the careless oversight of not yet having been born at the time.

The castle took 30 years to build and when Drewe died in 1931, it had only been completed for a year. And the roof leaked already.

Now the place is part-way through an £11 million project to finally sort that roof out. They’ve got the builders in big scale, having erected a massive scaffolding hangar around the castle. The stonemasons and builders work inside a mammoth tent, which you can enter by climbing a scaffolding tower. This is well worth the effort, for the view from the top and the gasp as you emit as you step inside a cathedral built from steel poles.

The other reason to visit is more surprising. Too often in these places, you pass from room to room and feel a yawn rising. All very fine but do we have to look at another old plate or read more about whatever rich person once owned this place?

Drogo is different – or it is for now. As most of the rooms are darkened so that the windows can be repaired, and as the place is basically a building site, the National Trust has done something unusually smart. The castle has been turned into an art installation built round the history of the building and the family.

The clever fun starts outside in a hut where you can learn about the argumentative ‘build’. “Will Julius Drewe ever finish on time and on budget?” as Kevin might ask, frowning in that way he has. “And will that roof ever stop dripping?”

Many angry letters were exchanged. You can read them here on an old typewriter with a digital screen attached. Press a button and the typewriter springs into noisy, clattering life and a copy of an original letter slides into view, as if being typed before your eyes. Much of this theatrical fun has been orchestrated by a company called Codsteaks, which worked with Aardman on the Pirates film.

Inside, each room is a fun puzzle or a smart and light-hearted artwork, with different artists taking charge of the displays. Everywhere is cleverly lit and wandering around the place is dreamlike, a bit like you’ve tumbled into a fairy story. And it’s all very amusing. The National Trust has a sense of humour – who knew?

In one room, there is one of those old-fashioned communications systems linking the different parts of the house. Press a button and voices emerge from the rooms, including Drewe having a rant. In the corner a jokey teasmaid-cum-radio broadcasts weather reports from inside Drogo, detailing the latest leaks.

There is much more inventiveness, including a display case containing a giant glass drip, the first one spotted by Drewe, it is said, and you go from room to room excitedly. Some rooms are imagined as if the place had really gone to rot; one contains a huge Char de Triomphe tapestry suspended from the ceiling so you can walk round it. Another room is stacked for storage, with puzzles and a hunt wrapped up in what’s on show.

No yawns here, and you leave feeling that you have connected to the place and the people. And that doesn’t always happen.