Ogof y Daren Cilau

Ogof y Daren Cilau is a cave system in the limestone escarpment on Mynydd Llangatwg (Llangattock Mountain), which is south of Llangattock village and above Crickhowell in south Powys, Wales. The escarpment is the remnant of quarrying that had begun by the mid-18th century and initially provided limestone for building and agriculture as a fertiliser, and subsequently for the blast furnaces of the local ironworks as a flux. The cave system was discovered in 1957 and is one of the longest in the United Kingdom. The system is next to the Ogof Agen Allwedd system.