Porth yr Ogof

Porth yr Ogof is a limestone cave system near Ystradfellte in Wales with multiple entrances and underground passages. The formation extends through the landscape along the Afon Mellte river, creating interconnected chambers and corridors.

Edward Lhuyd first documented the cave in 1698, establishing its importance for cave exploration in Wales. Later expeditions by local clubs in the 20th century expanded knowledge of its passages and formation.

The name comes from Welsh and means 'gateway to the cave', referring to its position in the Mellte Valley. Visitors can observe how the river Afon Mellte flows through the passages, shaping the cave's appearance daily.

Bring a torch and sturdy footwear to navigate safely through dark passages and uneven ground. A parking area is available near the entrance, and access on foot is possible when water levels are reasonable.

The main entrance stands as one of Britain's largest cave openings, with a broad, towering passage that draws water in from the river valley. This scale made the site historically easier for explorers to access compared to many other underground systems nearby.