This self-styled republic is not even on any natural land-mass, rather being located on an abandoned WWII radio/radar anti-aircraft embattlement in the North Sea, about seven miles off the southeastern English coast. I've always had an odd fascination with what I call the 'Tiny Nations of the World,' little quasi-fictitious governments that are not so terribly legal as they are annoying to try and legally depose/destroy or displace. Many of these tiny places were founded through legal 'loopholes' that have since been closed, thus grandfathering in these microstates.
This is one of my favorites, the Republic of Sealand.