Ogof Ffynnon Ddu (OFD) bottom entrance

You'll need proper caving gear and ideally a guide to explore this one - it's a serious underground system, not a walk-in tourist cave. Ogof Ffynnon Ddu stretches for miles beneath the Brecon Beacons, with the bottom entrance offering access to dramatic chambers, underground rivers, and passages that demand respect and experience.

The cave itself is genuinely impressive. Water-carved passages open into vast halls, and there's real geology on show - stalactites, flowstone, the works. It's the kind of place that reminds you why people get obsessed with caving. That said, this isn't for casual visitors or families expecting an hour's gentle exploration. You're looking at multi-hour expeditions that require fitness, proper equipment, and ideally guided access through an established caving club or operator.

If you're serious about it, contact the local caving club before turning up - access rules and conditions change. The nearest town is Swansea, though you're really in proper Beacons country here, surrounded by walking trails and moorland.

Stay at Brecon Beacons Camping & Caravan Park just down the road, or splash out on Four Falls Glamping or Aber Glamping if you want something with a bit more comfort after a day underground. Both five-star-rated and close enough to make it a natural base.

Bit of a specialist interest, but if you're into caving, it's world-class.