Sealand is one of the world's smallest micronations — though it is not recognised by the UK, it is effectively autonomous since it wasn't located in British territorial waters when it was established in the late 1960s.
It's off the coast of Essex, located 7.5 miles from Great Britain. The site was previously known as HM Fort Roughs, a military installation built during the Second World War.
As you can see, it's pretty small and isolated, with a helicopter platform taking up much of the space at the top of the building. Full-time military personnel were withdrawn from the structure in 1956.
It was part of a string of other defencive structures called the Maunsell Forts, built to protect south-eastern England against Nazi Germany's naval threat.
Here is HM Fort Roughs (now Sealand) being towed into place in 1942. The installation didn't begin being used for its current purpose until a quarter of a century later.
In 1967, former British army Major Roy Bates took over the fort with the idea of setting up a pirate radio station, keeping others who had the same idea at bay.
In 1967 Bates declared the "Principality of Sealand," declaring himself Prince Roy, and his wife Princess Joan. The fort has been effectively independent ever since.
Sealand has a red, black and white-striped flag, while the royal coat of arms says "E Mare Libertas" or "from the sea, freedom."
In 1987 the United Kingdom extended its territorial waters by 9 miles, and the area now includes Sealand. However, no serious challenge to the micronation's de-facto independence has been posed by London.
Some of the threats to Sealand's independence have come from the UK — in 1978 mercenaries employed by Alexander Achenbach invaded the island, but were eventually captured.
The fort issues its own currency, Sealand dollars, which are worth one US dollar. The ones they sell on their online shop, however, are slightly more expensive.
Sealand has also run a sideline business selling titles and stamps issued by the country. You can become a count or countess for £199.99 ($314.74), and get your own Sealand identity card for £25 ($39.34).
Michael Bates, son of Roy Bates, is Sealand's current regent. He was 14 when independence was declared. Roy Bates died at the age of 91 in 2012.
Prince James and Princess Charlotte of Sealand have carried on the royal line — they're pictured here meeting the BBC's Ben Fogle for the One Show.
The fort's main access to the rest of the world is by boats — which then have to be lifted up onto the top platform. There's also a helicopter platform.
Despite the harsh exterior, the inside is perfectly livable, if a little old-fashioned. At the time of the One Show's report on Sealand, the fort even had a resident cat.
Given the fort can sometimes be cut off by the choppy North Sea weather, there's quite a serious stock of tinned food on offer.
Sealand has picked up a cult following over the years — here's British climber Kenton Cool. unveiling the flag at the top of Mount Everest.
