I can’t explain why, in the face of all the seductive images and lyrical descriptions of the new Tintagel footbridge, I’ve become fixated on a small incision slashed through the surface of the walkway in the middle of the bridge. I know it’s technically the meeting point between the two cantilevered segments, a 40 mm expansion joint in an impeccably engineered structure. But it struck me forcibly that the seemingly reassuring surface connecting clifftop to clifftop, strung in tension over the dizzying void below, had been cut. It gave me a nervous charge. Was this an actual moment of the sublime?

The impossibly thin and fragile-looking bridge leads visitors, suspended as if on an ethereal spider’s thread, towards the mythical Cornish site where King Arthur, or at least the idea of him, was conceived. A fabulous king with little to support his claims needs all the fairy dust he can collect. And a bridge with a split in the middle is sheer effrontery but also total magic.

‘My Blue Heaven’ by John Christie, photograph © Nick Wood

Then I read about My Blue Heaven, John Christie’s corrugated iron shed, currently set down outside the pristine Sainsbury Centre for Visual Arts in Norwich, with related work on display indoors. And there it was, another gap. Christie’s little hut is raised off the ground, like Alexander Brodsky’s temporary pavilion in Bloomsbury Square two years ago. But you could, just, crawl underneath Brodsky’s pavilion, to read the poetry pinned on the interior walls. Christie’s tin shed, disconcertingly sundered into two unmatched halves, has no such wriggle room. There are no doors, no windows, just a slice through a skirt of crinkled galvanised iron that allows, as Christie writes, ‘the interior light and sound to escape more readily’. Ken Worpole in his catalogue essay says that My Blue Heaven evokes the tin tabernacles of eastern England; but the strong blue light and looped recording of Fats Domino at the piano suggest a different kind of enchantment.

The interior of Great Coxwell barn, photograph © Andy Marshall

I was also reminded of the immense monastic barns built in the Middle Ages to hoard agricultural loot. None is lovelier than Great Coxwell, pin-pricked with carefully positioned ventilation crannies: damp was the enemy of enterprise, so easily the undoing of all that wealth. William Morris thought the barn ‘as noble as a cathedral’. When the now empty interior dissolves into shadow, it is pierced by shafts of light, driving through the stonework and leaving the onlooker bewitched.

Tadao Ando’s late 20th-century Church of the Light is a few miles outside Osaka. The east wall consists of four unadorned blocks of masonry, their near junctures etching out a slender and luminous cross. Ando was inspired by Rome, specifically by the Pantheon, where the soaring coffered dome is sheared open, allowing the exterior elements – sunlight, rain, moonlight – to pour in, day or night, through the most resonant gap in all architecture.

The interior of the Pantheon, by Francesco Piranesi