The Brecon Beacons National Park encompasses some of the most important cave systems in Europe.
Geology and Cave Creation:
There are many outdoor centres and specialists in the Brecon Beacons which offer caving courses for the beginner and the more experienced caver, but be aware that caving is a potentially dangerous activity and the inexperienced should always have a qualified instructor or leader with them. Some of the more extensive cave systems in the National Park can only be accessed with the prior permission of local caving clubs and their experience is invaluable.
Geology and Landscape
The Carboniferous Limestone of south Wales was formed in shallow tropical seas over 300 million years ago. Much of it is of organic origin, being the shells and skeletons of sea creatures, large and small. Amongst the most spectacular fossils to be seen in the National Park are corals known as ‘Lithostrotion’. Their intricate internal detail is often beautifully preserved.
A band of this rock stretches across the National Park from Blorenge in the east to Carreg Cennen in the west. It’s in this thin belt of limestone country, 70km long but rarely more than 1km in width, that some of the most spectacular caves in Britain are to be found.
Limestone is soluble in mildly acidic water and the water running off the peaty ground of the National Park's hills is just that. Finding its way into small cracks in the rock, it widens them over the years creating a network of open fissures and tubes. When eventually these interconnecting passages reach a certain scale, we think of them as a cave network.
The caves form along both 'bedding planes' - the layers of rock themselves - and along vertical fractures present in the rock from the times millions of years ago when south Wales was successively stretched and squeezed as continents collided and split apart. Roof collapse also plays a part in the growth of a cave over many thousands of years.
Water pours down the southern slopes of the familiar Old Red Sandstone hills to the north and on meeting the limestone, disappears underground. Because most of the National Park's rocks slope gently towards the South Wales Coalfield, many caves follow this southward dip but they also extend east-west across it until they emerge in one of the major valleys carved through the limestone.
The Karst landscape
This countryside with its limestone pavements, caves, dry valleys and shakeholes is known as a 'karst' landscape after the classic region of that name in Slovenia. Our area differs from other karst areas of Britain in having fewer limestone pavements but many more shakeholes, particularly in areas that, at first sight, are not limestone areas. This is because though such areas as Mynydd Llangynidr and Mynydd Llangatwg are gritstone plateaux, the limestone isn’t far below the surface and the collapse of sections of cave within the limestone leads to craters appearing at the ground surface. Some are truly impressive at 60m across by 20m deep!
A taste of the underworld
All but a handful of the caves of the Brecon Beacons National Park are accessible only to the experienced caver with local knowledge or with the assistance of an expert local guide. The main exception is the extensive Dan-yr-Ogof system in the upper Swansea Valley. Here at the National Showcaves Centre, members of the public can taste the underground world of the National Park in safety. This very popular visitor attraction also has a café, Dinosaur Park, Iron Age Farm, Shire Horses and more.
A few miles further east in Waterfalls Country, visitors can stand in the impressive entrance of Porth yr Ogof where the entire Afon Mellte is swallowed by the earth. This, the largest cave entrance in the National Park, is below and adjacent to Cwm Porth car park albeit via a steep uneven twisting path. Visitors should not attempt to venture further than the immediate entrance of the cave and particular care should be taken during or following heavy rainfall as the cave entrance floods quickly and the footpath leading to the cave is especially hazardous when wet.
A small cave underneath Carreg Cennen Castle can be entered by visitors who bring a torch along with them – these can also be hired when you pay your entrance fee to the castle at the farm below.
The East of the Park
Some of the longest (and most tortuous) cave systems are found in the east of the National Park beneath Mynydd Llangatwg. Access to the major cave systems of Agen Allwedd and Ogof Daren Cilau is gained through entrances in the imposing Llangattock Escarpment across the Usk Valley from Crickhowell. Both drain ultimately into the Clydach Gorge, their combined resurgence being a deep pool known as Pwll y Cwm and of interest to the general visitor as well as the caver. A third major system, Ogof Craig a Ffynnon, can only be entered from its resurgence in the Clydach Gorge. Numerous other smaller caves have entrances both in the escarpment and the gorge.
Caves in Waterfall Country
Though less extensive than their cousins to east or west the cave networks around Ystradfellte and Penderyn are nevertheless very interesting.
Porth yr Ogof has already been mentioned but the Little Neath River Cave which takes the flow of the Nedd Fechan or Little Neath River is another important system. A view of the resurgence beside the Nedd Fechan known as Pwll Du or the ‘black hole’ (SN 912121) can be enjoyed by the non-caver taking the footpath upriver for a mile from the car park at Pont Melin-fach. An extraordinary swallow-hole is that of Pwll-y-felin beside the minor road between Penderyn and Ystradfellte (SN 942121). In wet weather the stream delivers water into this large crater faster than the cave beneath can take it away so it can fill to the brim.
There are a handful of small caves around Dinas Rock at Pontneddfechan and some in the valley of the Afon Hepste. The section of this river where Hepste Bridge crosses it (SN 945112) is dry in all but the wettest weather as its flow has retreated underground upstream at Ogof Glan Hepste.
Caves of the upper Swansea Valley
There are two major cave systems on either side of the valley not far from Craig-y-nos country park. Mention has been made of Dan-yr-Ogof (SN 838160), the 15km of which make it one of Britain’s most important caves. The impressive entrance series are open to the public but experienced cavers can explore substantial lengths of passage and magnificent chambers decorated with stalactites and stalagmites deep beneath the Black Mountain.
In 1912 two local men, Tommy and Jeff Morgan, decided to explore the cave entrance from which the River Llynfell emerges at the base of a cliff face. Their initial exploration of the cave ended when they reached a large underground lake. They returned to continue their exploration crossing the first lake and three others using a coracle which was small and light enough for their purposes. No further exploration of this complex system occurred until 1963 when Eileen Davies, a local member of the South Wales Caving Club managed to crawl through a tight passageway that had defeated earlier explorers.
Visitors to the show cave enter through a mined tunnel which gives access to a number of the areas originally discovered by the Morgan brothers including the large Cathedral Cave which is 10 m high at one point.
Walkers on the mountain above Dan yr Ogof can follow the course of the upper Afon Giedd to a point where the river sinks into its bed at (SN 811 180). Sinc y Giedd is the principal sink for the Dan yr Ogof cave system. Another impressive swallowhole also feeding water into this system is that at Waen Fignen Felen (SN 826177).
The other important system is Ogof Ffynnon Ddu which at 308m is Britain’s deepest cave. The Byfre Fechan stream sinks at Pwll Byfre (SN 875166) and emerges at Ffynnon Ddu itself at SN 846152. This cave is also Britain’s third longest with around 50km of passage. Walkers following the Beacons way across the Ogof Ffynnon Ddu national nature reserve are more or less tracing the line of the cave deep beneath them. Numerous small caves and shakeholes can be seen in this area.
West end of the Black Mountain
The Afon Llwchwr emerges dramatically from the limestone at Llygad Llwchwr, a major resurgence located at SN 669 178 and visible from a public foopath which passes nearby which provides water for the Brecon Carreg bottling company. This very wet cave was one of the first to be systematically explored when back in the 1840’s Thomas Jenkins of Llandeilo took a rope ladder and collapsible coracle into the cave.
There are a handful of other small caves in the west, the largest of which are in the Herbert’s Quarry area and include Ogof Foel Fawr and Ogof Pasg. Of most interest to the casual visitor is the cave accessible from within Carreg Cennen Castle which is itself perched on top of a magnificent limestone crag. This natural cave passage may have served as a water supply for the castle’s former occupants. Torches can be hired at the farm when paying Cadw’s entrance fee.
The inclusion in the list below of some clubs from further afield may seem odd but they have accommodation in the area and are very active in (or under!) the National Park:
The Westminster Speleological Group have a caving base at Penderyn and provide access for beginners to the caves of the area.
Outdoor adventure companies etc
Numerous companies offer underground adventure. They include the following:
Association of Caving Instructors – this website gives advice on hiring expertise.
• South Wales Caves is an excellent new interactive map-based site offering images of many of the cave systems of the ‘north crop’ – the band of limestone that passes through our area.
•www.cavinguk.co.uk/ is a personal page with all manner of interesting features and links including Caves in the Abergavenny area
British Cave Research Association is for those interested in the study of caves and their development.