Maunsell Forts, UK

Projected by the engineer Guy Maunsell and built in 1942 during the World War II on order by the Great Britain Royal Navy in the Thames Estuary Special Defence Units program, the sea forts were equipped with radar and anti-aircraft guns; they hosted over 100 soldiers each and their purpose was to protect the coast close to London from the attack of the German air force Luftwaffe and Navy.
During the war, these fortresses destroyed 22 German aircraft, 30 rockets and an S-Boot ship.

Now they stay abandoned since 1958 after a period in the mid-1960s when they were occupied by the first pirate radios like Radio Sutch, Radio City, Radio 390 and Radio Essex.