Ogof Cynnes

The entrance to Ogof Cynnes sits tucked into the hillside near Crickhowell, and you'll need a decent torch and proper footwear to make the most of it. This is a real cave - the sort where you actually crawl through passages and squeeze past rock formations, not a polished tourist operation with handrails and gift shops. The main chamber opens up reasonably well once you're inside, with stalactites hanging from the ceiling and a stream running through parts of it. It's small enough that you won't spend hours in here, but long enough to feel like you've properly explored something.

If you're into caving or geology, this scratches that itch. Casual visitors might find it a bit cramped and damp for their liking - there's no getting round the fact that it's muddy and you will get dirty. Children who don't mind a bit of grime and aren't claustrophobic will probably enjoy it, though younger kids might struggle with some of the tighter sections.

Access appears to be free, though it's worth checking locally as conditions can change. Allow an hour for a proper poke around without rushing. The cave sits within reach of the Black Mountains' walking routes, so it works well as a half-day addition to a wider Powys trip. If you're camping at Cwmdu Campsite nearby, it's a straightforward drive over and worth the detour if you've got the inclination for something off the beaten path.