Denge sound mirrors or listening ears. Concrete structures designed to pick up enemy aircraft coming from the channel. Built 1924 on Romney Marsh Stock Photo - Alamy
Denge sound mirrors | Sound Mirrors
These Enormous Concrete Acoustic Mirrors Pepper the British Coastline | ArchDaily
Britain's Sound Mirrors | Sound & Vision
These Enormous Concrete Acoustic Mirrors Pepper the British Coastline | ArchDaily
The concrete blocks that once protected Britain - BBC News