Ogof Ffynnon Ddu

Ogof Ffynnon Ddu is a limestone cave system in the Upper Swansea Valley in Wales. The network contains passages with underground streams, waterfalls, and deposits of stalactites and stalagmites formed over countless years.

Members of the South Wales Caving Club discovered this cave system in 1946, launching extensive explorations of its passages. These investigations revealed the geological importance of the site and expanded knowledge of Wales' underground landscapes.

The Welsh name translates to Cave of the Black Spring, referring to the underground waters that define the landscape. This name reflects how local people connect the place to the natural forces and features that shape what visitors see.

Access requires permits from the South Wales Caving Club and specialized equipment for exploring the passages. Visitors should prepare thoroughly before attempting to navigate this demanding underground environment.

The system reaches depths of 274 meters, making it the deepest cave in the entire United Kingdom. Its vertical scale sets it apart among Britain's other cave systems.

GPS coordinates: 51.82430,-3.66110

Latest update: December 9, 2025 18:47