When Louis XIV first proposed the idea of a fort in the middle of water off the Bay of Biscay, his advisors thought he had gone completely crazy. He was told the idea was impossible and was wisely dissuaded. 150 years later, Napoleon was on his charge across Europe and decided he was the right kind of crazy to actually build Fort Boyard.
Positioned between Île-d'Aix and Île d'Oléron, Fort Boyard was intended to make a blockade in the Strait of Antioch on the west coast of France. Ongoing disputes with the English made protecting French shores from their navy a priority. Unfortunately, actually building the fort became a logistic nightmare when construction was finally started in 1801.
Workers from local towns struggled miserably to set the stones needed for the foundations. The changing tides made placing and setting the stones a nearly impossible task. In 1809 the project was suspended for almost 30 years, until it was deemed that the British Royal Navy was still a major threat to France. In 1857, Fort Boyard was finally completed, but ironically was no longer useful. Cannon technology had improved and the Fort no longer served a strategic position in blocking attacks from the British Royal Navy.
When it was finally completed the fort stood 20 meters high, and had a length and width of 60 and 30 meters, respectively. Without any purpose for the massive fort, it quickly fell into disrepair, only briefly being used over the next 130 years. Finally, in 1988, restoration on the fort began with the intention of using the fort for an adventure game show, called "Fort Boyard."
Restoration work was quickly finished, and a support structure resembling an oil rig was built off the side of the fort to aid with the game show. In 1990, the game show began offering cash prizes for endurance challenges, and "Fort Boyard" began airing steadily across the world over the next 20 years. In many ways, the show was a precursor to better known physical game shows such as "Fear Factor." The show is still running today, and is the only way to get a look at Fort Boyard. You must be a contestant on the show to visit the island fortress, as it is not legally open to the public.