Dan-Yr-Ogof

The moment you descend into Dan-Yr-Ogof, the temperature drops and the outside world simply vanishes. Wales' largest cave system sprawls beneath the Brecon Beacons, a underground river flowing through chambers so vast your torch beam struggles to find the far wall. You walk through passages that have existed for millions of years, past stalactites and stalagmites that look properly alien in the darkness.

It's genuinely worth the drive from Swansea - about 45 minutes inland towards the mountains. The cave tour takes a couple of hours, so don't rush it. Families with children aged seven and up tend to get the most from it; younger kids sometimes find the darkness unsettling. History enthusiasts will appreciate that Bronze Age remains were discovered here - this wasn't just a cave, it was shelter.

The site includes a small museum and "Dinosaur Park" (a bit tacky, but kids don't mind). Admission isn't free, but it's reasonable. Go midweek if you can - weekends get crowded and echoing voices ruin the atmosphere.

If you're basing yourself at Brecon Beacons Camping & Caravan Park - which is practically on the doorstep - combine this with a proper walk up Pen y Ghent or along the Waterfall Walk nearby. Dan-Yr-Ogof works brilliantly as a rainy-day backup or a morning visit before hiking. Aber Glamping and Four Falls Glamping are closer to Swansea but still within 20 minutes, making this a solid addition to any Beacons break.