Ogof Craig a Ffynnon (Welsh for "Rock and Fountain Cave") is a cave in Wales. The cave is about 3 km in length, making it currently the sixth longest known cave in Wales and the tenth longest cave in the United Kingdom . 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 calcite formations. 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.