Dan yr Ogof, also known as the National Showcaves Centre for Wales, is a 17-kilometre (11 mi) long cave system in south Wales, five miles north of Ystradgynlais and fifteen miles south west of Brecon within the Brecon Beacons National Park. It is the main feature of a show cave complex, which is claimed to be the largest in Europe and is one of the major tourist attractions in Wales.