Shell Grotto

A underground tunnel lined entirely with shells - that's Shell Grotto near Truro, and it's genuinely odd in the best way. You're walking through a narrow passage with thousands of shells pressed into the walls and ceiling, creating this glittering, almost alien landscape a few metres below ground. The whole thing takes about twenty minutes to explore, though you'll probably spend longer staring at the detail work.

Originally built in the 18th century as a folly (basically a Victorian rich person's conversation piece), it's one of those attractions that sounds gimmicky until you're actually down there. Then it just feels properly strange and atmospheric. The shells catch the light in ways you don't expect, and there's something hypnotic about the repetitive patterns.

It's not a massive undertaking - families with young kids will either love the novelty or find it claustrophobic, so know your children. History buffs and anyone into industrial archaeology will find it interesting; casual tourists might feel it's a bit of a detour. Allow an hour including the walk around the site.

If you're based at Trethem Mill Touring Park or Stay Wild, it's only a short drive into Truro, making it an easy morning activity before heading to one of Cornwall's bigger attractions. The grotto works best on a quiet day - avoid school holidays if you want to appreciate the oddness without queuing. Check ahead for opening times as they can be unpredictable, and bring a torch - the lighting is atmospheric rather than bright.