Caves
The Brecon Beacons National Park encompasses some of the most important cave systems in Europe. All but a handful of the caves in these systems are the sole preserve of the experienced caver, but certain sections are much easier to access. The National Showcaves Centre for Wales at Dan-yr-Ogof is a fantastic place to start.
If you’d like to explore more extensively, you may need the permission of a local club and the assistance of a qualified instructor or leader.