Dan yr Ogof (Welsh pronunciation: [ˈdan ər ˈoːɡɔv]), at the National Showcaves Centre for Wales, is a 17-kilometre (11 mi) long cave system in south Wales, about 5 miles (8 km) north of Ystradgynlais and 15 miles (24 km) southwest of Brecon, in the Brecon Beacons National Park. It is the main feature of a show cave complex, which is claimed to be the largest in the UK and is a tourist attraction in Wales.