Porth yr Ogof is a

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

located near the village of

Ystradfellte Ystradfellte is a village and community in Powys, Wales, about north of Hirwaun, with 556 inhabitants. It belongs to the historic county of Brecknockshire (Breconshire) and the Fforest Fawr area of the Brecon Beacons National Park, beside the Af ...

, near the southern boundary of the

Brecon Beacons National Park The Brecon Beacons National Park ( cy, Parc Cenedlaethol Bannau Brycheiniog) is one of three national parks in Wales, and is centred on the Brecon Beacons range of hills in southern Wales. It includes the Black Mountain ( cy, Y Mynydd Du) in ...

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. It lies on the course of the

Afon Mellte Afon Mellte or the River Mellte is a river in south Wales. It is formed by the confluence of the Afon Llia and the Afon Dringarth. It then flows south through the village of Ystradfellte to Pontneddfechan where it joins with the Nedd Fechan ...

, a river whose name translates as ‘lightning’, commonly explained as a reference to the flashy' nature of the river, i.e. rising and falling rapidly in response to rainfall. In 1998 the cave's passageways had been measured as over in length. Among the cave's fifteen entrances is the largest cave entrance in Wales and one of the largest in the UK standing at nearly wide and high. The cave was used as a

show cave A show cave—also called tourist cave, public cave, and, in the United States, commercial cave—is a cave which has been made accessible to the public for guided visits. Definition A show cave is a cave that has been made accessible to ...

many years ago, but is not as attractive as more decorated caves such as

Dan yr Ogof Dan yr Ogof (), at the National Showcaves Centre for Wales, is a long cave system in south Wales, about north of Ystradgynlais and southwest of Brecon, in the Brecon Beacons National Park. It is the main feature of a show cave complex, wh ...

, and so today is more often used to introduce people to cave exploration.

Cave features

Porth yr Ogof is most often entered through the wide main entrance, either using a dry ledge on the left or by wading through the knee-deep river to the centre and right. The second most used entrance is called the Workman's or Tradesman's Entrance. A passage in the left of this entrance leads to a mud cavern. Challenging elements of the cave interior include the "Wormhole" (a curving crawl tube on the right wall of the main entrance), the "Letterbox" (a rectangular space in the passage) and the "Creek", further inside the cave. There are also two features named the "Washing Machine", both of which feature large expanses of water. Porth yr Ogof is now uncommercialised, and is used as a training cave for caving. There are two short

pothole A pothole is a depression in a road surface, usually asphalt pavement, where traffic has removed broken pieces of the pavement. It is usually the result of water in the underlying soil structure and traffic passing over the affected area. Wat ...

s easily accessible to amateur potholers. The cave is generally wet. White Horse Pool, named after the shape of the calcite deposit on the back wall, is several metres in depth despite the shallowness of the edges, and there are many

sump A sump is a low space that collects often undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers. Sump can also refer to an area in a cav ...

s (completely flooded passageways), the majority of which exist in the portions of the cave north of the Tradesman's Entrance.

Deaths

Porth yr Ogof resurgence in flood conditions

There have been eleven deaths at Porth yr Ogof since 1957, ten of which occurred in the cold, fast-flowing and deep Resurgence Pool at the far end of the cave where the Afon Mellte resurges.

Geological and human history

'Porth yr Ogof' is

Welsh Welsh may refer to: Related to Wales * Welsh, referring or related to Wales * Welsh language, a Brittonic Celtic language spoken in Wales * Welsh people People * Welsh (surname) * Sometimes used as a synonym for the ancient Britons (Celtic peopl ...

, translated as 'gateway to the cave'. The cave lies in the valley of the

and is located in a comparatively narrow band of

Carboniferous Limestone Carboniferous Limestone is a collective term for the succession of limestones occurring widely throughout Great Britain and Ireland that were deposited during the Dinantian Epoch of the Carboniferous Period. These rocks formed between 363 ...

. Except after periods of heavy rain, the river bed is largely dry downstream of Ystradfellte, the river only rising to the surface again just before the cave. The cave has been known to humans for many centuries, but because of the passageway's susceptibility to severe flooding there has been no evidence found of any

prehistoric Prehistory, also known as pre-literary history, is the period of human history between the use of the first stone tools by hominins 3.3 million years ago and the beginning of recorded history with the invention of writing systems. The use o ...

human habitation. The cave and its many visible

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s were mentioned in the writings of

Edward Lhuyd Edward Lhuyd FRS (; occasionally written Llwyd in line with modern Welsh orthography, 1660 – 30 June 1709) was a Welsh naturalist, botanist, linguist, geographer and antiquary. He is also named in a Latinate form as Eduardus Luidius. Life ...

, and in the 19th century it was mentioned again by the first pioneers of caving.

References

{{reflist Tourist attractions in Powys Caves of Powys Fforest Fawr Closed show caves in the United Kingdom