Sound Mirrors

You'd be forgiven for thinking these were either purpose-built sculptures, satellite dishes from an ancient civilisation or some kind of alien apparatus. They are, in fact, concrete sound mirrors, an early form of radar. Made to detect approaching enemy aircraft, they were soon made obsolete when radar was introduced in the 1930s.

Built in the early part of the 20th century, sound or acoustic mirrors were littered along the English coast, the most famous remaining ones (three of them, pictured) can be seen at Denge in Kent. (If you are in the area it's well worth popping to nearby desolate Dungeness with its bleak landscape, nuclear power station, black wooden houses and Derek Jarman's garden, now owned by his surviving partner. Dungeness is one of the largest shingle areas in the world and has unique flora and fauna.)

There's no public access to the mirrors, so a guided walk is the only way to see them – they are now surrounded by a moat and a usually locked swing bridge is opened a couple of times a year for visitors. My boon companion and I arrived late (even though we were travelling at 90mph in an Alfa Romeo Sprint) and hastened across the shingles and pebbles to find the group. We came across more lost people, who at least had a map and compass, and between us we found the group just as they were about to close the bridge to the mirrors. Make no mistake, they are pretty difficult to find (they're in an old gravel pit in the middle of nowhere); you don't really see them in the distance, then suddenly they're right in front of you, and there is a feeling akin to stumbling upon, say, Borobudur, Angkor Wat or some other relic of a lost civilisation.

Further details here.