Background

Porth yr Ogof: Wales' Largest Cave Gateway in Brecon Beacons

Explore Wales’ largest cave entrance, a thrilling limestone labyrinth carved by the Afon Mellte in the heart of Brecon Beacons National Park.

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Porth yr Ogof is a vast solutional cave near Ystradfellte, Wales, boasting the largest cave entrance in Wales and one of the largest in the UK. Stretching over 2.25 km, this limestone cave system features multiple entrances, underground rivers, and striking geological formations. Once a show cave, it now serves as a premier site for caving exploration and training in the scenic Brecon Beacons National Park.

A brief summary to Porth yr Ogof

  • Aberdare, Ystradfellte, CF44 9JF, GB
  • Duration: 1 to 3 hours
  • Budget
  • Environment icon Outdoor
  • Mobile reception: 3 out of 5
  • Monday 12 am-12 am
  • Tuesday 12 am-12 am
  • Wednesday 12 am-12 am
  • Thursday 12 am-12 am
  • Friday 12 am-12 am
  • Saturday 12 am-12 am
  • Sunday 12 am-12 am

Local tips

  • Wear sturdy waterproof footwear as parts of the cave require wading through knee-deep water.
  • Join a guided caving tour or training session to safely explore the cave’s complex passages.
  • Avoid the Resurgence Pool area due to its depth and strong currents; heed all safety signage.
  • Visit during drier weather for easier access, as the cave can be very wet and slippery after rain.
  • Combine your visit with a walk along the scenic Afon Mellte gorge to experience the surrounding natural beauty.
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Getting There

  • Car

    Drive from Brecon via the A4059 towards Ystradfellte, approximately 40–50 minutes. Parking is available at the Porth yr Ogof pay & display car park near the cave entrance. Note that parking fees apply and spaces can fill during peak times.

  • Bus

    Take the local bus service from Brecon to Ystradfellte, which takes about 1 to 1.5 hours depending on the schedule. From Ystradfellte village, it’s a 20-minute walk along marked trails to the cave entrance. Bus services may be limited on weekends and holidays.

  • Walking

    For those staying nearby, a scenic 30–45 minute walk from the Waterfalls Centre in Pontneddfechan follows well-maintained trails through the Afon Mellte gorge to Porth yr Ogof. Terrain includes rocky paths and some uneven surfaces, suitable for moderately fit walkers.

Porth yr Ogof location weather suitability

  • Weather icon Any Weather
  • Weather icon Rain / Wet Weather
  • Weather icon Mild Temperatures

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Discover more about Porth yr Ogof

A Majestic Entrance to the Subterranean World

Porth yr Ogof, meaning 'gateway to the cave' in Welsh, is renowned for having the largest cave entrance in Wales, measuring nearly 20 meters wide and 8 meters high. Located near the village of Ystradfellte at the southern edge of the Brecon Beacons National Park, this imposing gateway invites adventurers into a vast limestone cave system carved by the Afon Mellte river. The river’s flashy nature, rising and falling rapidly after rainfall, plays a key role in shaping the cave’s dynamic environment.

Complex Network of Passages and Entrances

The cave extends over 2.25 kilometers with more than fifteen entrances scattered around the area. The main entrance is typically accessed by a dry ledge or by wading through knee-deep river water, while other notable entrances like the Workman's or Tradesman's Entrance provide alternative access points. Inside, visitors encounter a labyrinth of passages, including boulder-strewn floors, calcite pools such as the White Horse Pool, and underground waterways. The cave is largely wet, with several sumps—completely flooded passages—that challenge even experienced cavers.

Historical and Geological Significance

Porth yr Ogof has been known since at least the late 17th century, mentioned by naturalist Edward Lhuyd and explored extensively in the 20th century by pioneering caving clubs. The cave’s passages are formed within Carboniferous Limestone, a geological formation stretching across the Brecon Beacons. The area is rich in fossils and features remarkable calcite veins and stalactites, providing insight into the region’s ancient natural history.

A Hub for Caving Enthusiasts and Training

While once operated as a commercial show cave, Porth yr Ogof now serves primarily as a training ground for cavers of all skill levels. Its varied terrain includes crawls, climbs, and water-filled sections, making it an ideal primer for cave exploration. Safety is paramount, as the cave has a history of accidents, particularly near the deep and fast-flowing Resurgence Pool. Guided excursions emphasize the cave’s unique features such as Hywel’s Grotto, a chamber adorned with calcite formations and pools.

Natural Beauty and Conservation

Surrounded by the lush, fern-covered gorge of the Afon Mellte, the cave lies within a Special Area of Conservation and a Site of Special Scientific Interest. The area’s magical atmosphere has attracted filmmakers and nature lovers alike. Visitors can appreciate not only the subterranean wonders but also the scenic landscapes and wildlife of the Brecon Beacons National Park.

Visitor Experience and Practical Details

Exploring Porth yr Ogof offers a blend of adventure and natural history. The cave’s large entrance and accessible passages make it suitable for beginners accompanied by experts, while experienced cavers can delve deeper into its maze-like network. The nearby Waterfalls Centre provides visitor facilities, and the surrounding trails offer opportunities for hiking and wildlife observation. The cave’s wet and sometimes challenging conditions require appropriate preparation and respect for its natural hazards.

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