Some views of the three experimental sound mirrors at Denge near Dungeness. When I first visited you could walk out to them (in the middle of a gravel pit). There is no longer any mining there and a swing bridge keeps the island with the mirrors on secure. They were built as a way of listening out for and locating hostile aeroplanes. but they were made redundant by the emerging radar technologies. There are a few more dotted along the coast. The largest mirror (to the left in the bottom view) is 200 feet across.