Ogof Agen Allwedd or Agen Allwedd, is, at 20.2 miles, one of the longest cave systems in Wales, and the longest cave system on the Llangattock escarpment.

A cave gate is a manmade barricade typically placed at, or just inside, the entrance to a cave in an effort to impede or mitigate human access to a cave's interior. The reason for gating a cave can be