Maunsell Sea & Air Forts, Thames and Mersey estuaries, United Kingdom
During World War II, the Maunsell Army Sea & Air Forts were built to defend England against German forces.
A group of forts raised above the water on stilts made up the complex, designed by Guy Maunsell, a British civil engineer.
The forts officially closed in the 1950s, but the structures that remain can occasionally be seen from land at East Beach Park in Southend-on-Sea.