Between the villages of Pontneddfechan and Ystradfellte is a series of dramatic waterfalls, where the Rivers Mellte, Hepste and Pyrddin pass through steep forested gorges. The finest is Sgwd-yr-Eira (Waterfall of the Snow), where you can actually walk behind the torrent. At one point the River Mellte disappears into Porth-yr-Ogof (Door to the Cave), the biggest cave entrance in Britain (3m high and 20m wide), only to reappear 100m further south.
Walks in the area are outlined on the national park's Wood of the Waterfalls walk card (£1), available from visitor centres.
