Otter Hole

Otter Hole is a cave in Monmouthshire, just north of Chepstow on the Wales–England border. It runs beneath the Chepstow Racecourse from the banks of the tidal River Wye. The cave contains many decorated chambers filled with cave formations. Access is controlled by the Royal Forest of Dean Caving Club on behalf of the landowner. The entrance is a gated doorway at the foot of a bluff on the riverbank. The cave is known for its rare and well-decorated formations, making it one of Europe’s finest examples. The route includes a tidal sump that blocks access except at low tide. Two trips are possible: a six-hour ‘between tide trip’ or a nine-to-fifteen-hour ‘overtide trip’. Beyond the sump, a streamway leads to chambers like the Hall of 30, the largest decorated space. Its stalagmites range from white to black, coloured by minerals in the bedrock. Visitors follow a linear route along the streamway, sometimes removing mud before reaching the Hall of 30. The cave’s far reaches, known as Camp, hold delicate formations like straws and helictites. All trips are guided by wardens from the Royal Forest of Dean Caving Club. Conservation work is part of the visit, including cleaning formations and removing litter. The cave is a Site of Special Scientific Interest, protected for its unique features.