The Grotto

Down a wooded slope near Lydney, there's a sandstone cave carved into the hillside that locals call The Grotto - and it's one of those spots that feels genuinely forgotten. Built in the 18th century as a folly, it's nothing fancy: just a small chamber with a bit of stonework, the kind of thing a Victorian gentleman might have knocked up to impress house guests. You'll need to pick your way through trees and rough ground to reach it, so proper walking boots matter more than the attraction itself.

The real appeal is the walk rather than any grand reveal. It takes perhaps twenty minutes to find it if you know where you're going, and another ten to poke around inside. Kids aged eight upwards will find it interesting enough - there's something about exploring a cave that never gets old - but expect a quarter-hour's amusement max. Bring a torch; the light inside is rubbish.

What makes it worth the effort is context. Pair it with a day circuit around Monmouthshire's proper attractions, or use it as a leg-stretcher during a longer walk. If you're based at Penhein Glamping five miles away, it's a decent afternoon diversion on a grey day. Free, obviously. Nobody charges for overgrown holes. Go when it's dry though - the path gets boggy.