During the Second World War, the British Royal Navy constructed a series of sea forts for an advanced line of defense against inbound air raids and potential sea invasions from the Axis powers. The Maunsell Sea Forts still stand today, silent and abandoned a few meters above the North Sea. One, however, remains inhabited, now a nation of its own referred to as the Principality of Sealand.
I recently encountered a very strange person who claimed to be a citizen of Sealand. He even had a passport and a noble title.