Sealand, the abandoned forts off Britain’s coast

The BBC has an article (with its usual unbloggable video, containing much more info) about the World War Two-era anti-aircraft forts in the Thames:

If you venture just seven miles off the British coast, to a place called Red Sands, you will encounter an unusual sight: giant towers rising from the ocean on rusted legs. They look almost alien, but are actually a relic of Britain’s military past: the Maunsell Forts.
Built in the Thames Estuary to defend the United Kingdom from air raids during World War Two, the forts have been decommissioned for more than fifty years. Delicate and at risk, they are usually off-limits to the public, but we got special access with the help of a group of passionate volunteers, flying a drone around the strange structures, learning about their surprising history and seeing the ambitious project trying to secure their future.

Rico says we have stuff like them in the US, but not sitting out in the river like these are (unless you count Alcatraz), but there's a lot to see here...