The sign says:
Lydford Castle was probably built about 1195 to serve as a prison. It took the form of a freestanding tower of at least two storeys. Sometime in the thirteenth century a thorough rebuilding was undertaken. A ditch was dug around the tower and the soil piled up against the ground floor. The upper storeys were completely rebuilt to form a small keep and the interior of the old prison filled in (this filling has now been removed). At the same time the earthwork bailey to the North West was constructed.
The property is managed by the National Trust in co-operation with English Heritage.
(
visit link)