Some buildings are just bizarrely intriguing because they look like something out of a science fiction movie - instead of looking like a practical building. The Maunsell Sea Forts (a.k.a. Thames Estuary Army Forts), for example. They were built in the second world war, to provide anti-aircraft fire in the Thames estuary. Each fort consisted of a group of seven towers with a walkway connecting them all to the central control tower. The fort, when viewed as a whole, comprised one Bofors tower, a control tower, four gun towers and a searchlight tower. They were arranged in a very specific way, with the control tower at the centre, the Bofors and gun towers arranged in a semi-circular fashion around it and the searchlight tower positioned further away, but still linked directly to the control tower via a walkway. All the forts followed this plan and, in order of grounding, were called the Nore Army Fort, the Red Sands Army Fort and finally the Shivering Sands Army Fort.
The buildings definitely served their purpose, but the question was what would happen to it after wartime. One of the three forts (Nore) was dismantled in 1959, but the other two are still standing nowadays. They functioned as pirate radio stations in the seventies and sixties, but now they are just standing there, defunct - and just look freaky.
More information about the sea forts can be found here.
and there are a whole bunch of photos to be found on flickr.