|Location||North of Blaenavon, Wales|
|Length||66 kilometres (41.0 mi)|
|Access||Pwll Du Cave Management Group.|
|Translation||Hawthorn Cave (Welsh)|
|Cave survey||OUCC survey information|
Ogof Draenen (Welsh for Hawthorn Cave) is, at 66 km (official figure; the true length of passage is still being revised upward, with a rough modern approximation at it being 70 km), the longest cave system in Wales and the second longest in Great Britain behind the Easegill System, Lost John's Cave and Notts Pot system on the Cumbria/Lancashire border.
The cave was known only as a small entrance on a steep hillside until several years of digging broke through into major passage development in October 1994. It was then explored at unprecedented speed to become the longest cave in Wales.
Draenen contains a variety of spectacular decorations and some huge passages (the War of the Worlds section is probably the second largest cave passage in Britain). Its large size and occasional complexity make the cave a challenge for even experienced cavers.
- Wilton-Jones, Mark (17 April 2013). "Ogof Draenen description". cavinguk.co.uk. Retrieved 5 January 2014.
- "Three Counties System Connects to Create UK’s First 100 Kilometre Cave System". Caving News. 7 November 2011. Retrieved 5 January 2014.
- "Aims of the Group". Pwll Du Cave Management Group. Retrieved 5 January 2014.