Ogof Agen Allwedd

Ogof Agen Allwedd or Agen Allwed, also known as Aggy, is, at 32½ km long, one of the longest cave systems in Wales, and the longest cave system on the Llangattock escarpment, where Ogof y Daren Cilau is also found.

There are several round trips that can be followed within the system, but all trips start via the short entrance series and first boulder choke, which is mostly easy caving. The round trips include the Grand Circle - along Main Stream Passage, which has four boulder chokes (areas of severe breakdown) in it, and Southern Stream Passage, a long, wet and tedious passage. There are also the Outer and the Inner Circles, which include Turkey Streamway; with some formations including gour pools.

Some new extensions to Agen Allwedd contain particularly fine formations. Agen Allwedd is also important due to the numbers of bats that roost there. Bats are strictly protected from disturbance under the Wildlife & Countryside Act 1981, the Habitat Regulations 1994 and the EC Habitats Directive. It is a criminal offence to deliberately or recklessly disturb bats. Cavers should take care to avoid causing disturbance.

Originally, the cave was accessed through the Agen Allwedd entrance, but gated access is now available through the Ogof Gam entrance. This provides a bypass to an awkward rift and that route is now blocked with a pillar.