Hey, it’s just beautiful outside right now. The sun is warm. The gorse is in full bloom along the Hampshire verges, with the oilseed rape and the hawthorn blossom it’s glorious against the clear sky. And in my garden primroses are still exuberant and pear blossom and bluebells are joining the show.

At this time of year I always get restless and want to go travelling. Don’t know why, maybe it’s the Viking genes. I want to see the sea. I want to get into my longship and raid Lindisfarne. Which is not easy when you live in Berkshire.

So I went for a drive instead – out to Salisbury and had a wander around the cathedral.

I really recommend the behind-the-scenes tours. The cathedral website calls them ‘tower tours’ which does not do justice to how wide-ranging and brilliant they are. You get to see the cathedral from totally different viewpoints, up some winding stairs to look out over the nave from a high balcony just beside a medieval stained glass window. You can ascend to the space in the roof of the nave and walk along the rafters above its ceiling, which are all massive thirteenth-century timbers. Then into the tower, you can envisage how it was built, there are three floors to ascend, and you can look up into the inside of the spire - to see the original scaffolding spiralling up elegantly inside. You can gaze out of the spire balconies (I love heights) to the cloisters, the cathedral court and the country around.

My favourite though was an original wooden treadmill used for raising blocks of stone. It’s still in the same place and has the carpenter’s marks on its planks. Walking in a treadmill to haul up masonry on the exposed summit of a 400ft unfinished tower – in the rain – must have been one of the least popular jobs of 1330, even though they did consider their work a gift to God.

The treadwheel in the spire

The tour took two hours - necessary because the hidden wealth in the cathedral’s roof space is as impressive as the arches and carvings of the nave. The knowledgeable tour guide pours out mind-blowing facts: a clock dating from 1386 and still ticking, the harder stone for the basement to prevent the tower crushing the foundations, the girders added by Christopher Wrenn because the medieval braces began to look flimsy to hold up six and a half thousand tons of stone. In the fourteenth century they were forged from farmer's ploughs because metal supplies ran short – but in true medieval style, they decorated every girder.

The West Front of Salisbury Cathedral, with all its statues, is close to how I envisage the North Façade of the Emperor’s Throne Room. With Winchester, Ely and Durham Cathedrals, York Minster, King’s College Chapel in Cambridge, the Divinity School in Oxford and – oh, lots of other buildings – I used Salisbury Cathedral to imagine the Emperor’s Palace in the heart of the Castle. It’s a gothic hall, (once the palace of the Pentadrica) and the classical and renaissance buildings surrounding it are all contained inside the formidable, massive curtain wall of the Castle itself. The Castle’s outer wall, with its imposing three gateways looks like the very strongest medieval fortress – except that you can see the palace spire and roofs towering up from inside.

It would be vulnerable from the air, though, which Geo makes use of in No Present Like Time.

I’ll tell you more about the fortified outside walls of the Castle next time I visit one of the medieval castles which has been an influence.

Went gliding with The Vale of the White Horse Gliding school. Two sessions in the air - no thermals so when we were towed up to 2000m we had twenty minutes to glide back down but I tried a few turns and some flying on the straight.

It was a one-off birthday present left over from last February (thanks, Brian). This was the first chance I had, owing to writing The Modern World. It was well worth the wait.

The best bit is being released from the tug plane - sudden silence and a wonderful feeling of lightness. I could tell from the strain in the instructor's voice that I was making the turns rather too steep. Oh, and the way the ground kept tilting up.

I love being airborne - balloons, helicopters, parachuting, anything - and I've always used the experiences to help describe Jant's flight in the Castle books.

In the glider cockpit, waiting for the tug plane