Porth yr Ogof

Porth yr Ogof is a cave near the village of Ystradfellte on the edge of the Brecon Beacons National Park in Wales. It sits on the Afon Mellte, a river that rises and falls quickly after rain. The cave has fifteen entrances, the largest of which is nearly twenty metres wide and eight metres high. In 1998 its passageways measured over two and a quarter kilometres long. Once used as a show cave, it now introduces people to cave exploration. The name means ‘gateway to the cave’ in Welsh. The cave is known for features like the Wormhole, a curving crawl tube, and the Letterbox, a rectangular space in the passage. White Horse Pool is several metres deep despite shallow edges, and the Resurgence Pool at the far end is seven metres deep. There are also two Washing Machines, large expanses of water, and many completely flooded passageways called sumps. Eleven deaths have occurred here since 1957, most in the Resurgence Pool. Visitors enter through the wide main entrance, either on a dry ledge or by wading through knee-deep water. The Workman’s Entrance leads to a mud cavern, and two short pothole entrances are open to cavers. The cave is generally wet, with fossils visible in the limestone walls. Edward Lhuyd wrote about the cave in the 17th century, and 19th-century caving pioneers like T.A.J. Braithwaite also mentioned it. Today it remains uncommercialised and is used for training.