Ogof Craig a Ffynnon (Welsh for Rock and Fountain Cave) is a cave of around 13 km in length, making it currently the 6th longest in Wales and 10th in the UK. The cave is renowned as one of the most well-decorated caves in Britain.
The cave contains some early short crawling sections and some wet passages with voluminous quantities of mud before developing into a series of large sections lavishly decorated with mud and calciteformations. The most spectacular of these is the Hall of the Mountain Kings, a large cavern liberally adorned with flowstone.
Beyond the well-decorated section the cave continues in a long series of low passages. It is thought that the cave will eventually be connected to the theoretical Llangattock System through Ogof y Daren Cilau.
Access to the cave is controlled by the Grwp Ogofydd Craig A Ffynnon.