Caer Llan is a field studies centre, conference centre and former country house located at Lydart within the community of Mitchel Troy, Monmouthshire, south east Wales, about 3 miles (4.8 km) south-west of Monmouth. It is close to the top of a scarp slope with extensive views westwards over the valley of the River Trothy, and is accessed from the B4293 road.