Porth yr Ogof

Porth yr Ogof is a river cave beside the village of Ystradfellte in Wales, close to the southern edge of Bannau Brycheiniog (Brecon Beacons) National Park. The Afon Mellte flows through it, and the cave sits in the heart of Waterfall Country.

What is Porth yr Ogof?

The cave formed as water dissolved the surrounding rock. Here the Mellte slips underground and re-emerges further down the valley. The river's Welsh name means "lightning", a nod to how fast it swells and drops after rain. A 1998 survey measured more than 2.25 km of passages. The cave has fifteen entrances, and the biggest, roughly 20 m wide and 8 m high, is the largest cave mouth in Wales and among the biggest in the UK.

It was once opened to paying visitors, but its interior is plainer than that of showpiece caves such as Dan yr Ogof. Today it mostly serves as a first taste of caving for beginners with guides.

What will you see?

The entrance arch is the highlight: a vast opening in the rock with the river running through it. Most visitors stay at the entrance and on the footpaths. The interior is for experienced cavers, because water levels can climb fast after rainfall.

How do you get there?

The nearest parking is the national park car park at Cwm Porth, where a signed path leads down to the cave. The descent is steep and the rocks can be slippery, so wear sturdy boots. Entry to the cave is free, but parking is charged. Check the current rate on site or with the park authority. A car is the easiest way to reach this remote corner of the park.

How long do you need, and what can you combine it with?

Seeing the cave takes under an hour. The path continues south and joins the Four Waterfalls Loop, a popular route past falls on the Mellte, Hepste and Pyrddin. The full circuit is about 10 km and takes around four hours.

When should you visit?

Weekends and bank holidays in fine weather get crowded, so a weekday is calmer. Avoid the cave after heavy rain, when the river rises quickly.

Frequently asked questions

Is there an entrance fee? No. The cave is free to see; you pay only for parking at Cwm Porth.

Can I go inside the cave? Visitors mainly view the entrance and nearby paths. Going deeper takes experience and equipment, and the river current can be dangerous.

How long does a visit take? Under an hour for the cave itself, or about four hours combined with the Four Waterfalls Loop.

Is it wheelchair accessible? No. The path is steep and uneven, and the setting is rural.