Dungeness and the Sound Mirrors

Dungeness is one of the largest areas of shingle in the world, and of international conservation importance for its unique variety of wildlife. These structures were built between the wars and formed part of an early warning system designed to detect the sound of distant enemy aircraft approaching the Kent coast. The sound of the aircraft engines would be reflected in the curved surfaces and concentrated onto a central microphone. The development of faster aircraft and invention of the radar eventually made them obsolete. The mirrors are located on private land, but guided tours are available. More details here.