Porth yr Ogof

Porth yr Ogof is a solutional cave near the village of Ystradfellte, near the southern boundary of the Brecon Beacons National Park in Wales. It lies on the course of the Afon Mellte, a river whose name translates as 'lightning', commonly explained as a reference to the "flashy" nature of the river, i.e. its rising and falling rapidly in response to rainfall. In 1998 the cave's passageways had been measured as over 2.25 kilometres (1.40 mi) in length. Among the cave's fifteen entrances is the largest cave entrance in Wales and one of the largest in the UK, nearly 20 metres (66 ft) wide and 8 metres (26 ft) high. The cave was used as a show cave many years ago, but is not as attractive as more decorated caves such as Dan yr Ogof, and so today is more often used to introduce people to cave exploration.