Today I was doing some reading about the little known offshore defense system England built during the Second World War. 

Effectively they built a string of these really weird looking structures in the waters off the shore to protest shipping lanes as well as create a first line defense against air raids. 

Just looking at the pictures is surreal - don't think you'll see anything like this anywhere

Read details and see pictures here:

http://diamondgeezer.blogspot.com/2008_09_01_archive.html#8970900984368410875

http://subterrain.org.uk/maunsell/part2.html

http://www.undergroundkent.co.uk/maunsell_towers.htm