A series of dramatic falls lies between the villages of Pontneddfechan and Ystradfellte, 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.
The gentle Elidir Trail (2½ miles each way) starts from Pontneddfechan and connects with various other trails. Take special care – the footpaths can be slippery, and there are several steep, stony sections. The Four Falls walk, which takes in everything, is a hard 5.5 miles and demands proper footwear.
