During WWII, British scientists were performing biological warfare experiments. The setting for the tests was Gruinard Island, a mile off the coast of Scotland. The idyllic island was then placed under quarantine for the next 50 years.
Gruinard Island was chosen as a site because it was small and uninhabited. The British government brought 80 sheep to the island. Anthrax bombs were detonated near the animals, and they died within several days. The anthrax led to an extremely deadly disease affecting the lungs, bowels and skin.
The tests showed that the bombs would kill British enemies quickly, but the indestructible anthrax spores would leave cities uninhabitable for decades. The fallout meant Gruinard Island had to be quarantined. Any visitor would be infected.
In 1981, a group of rogue microbiologists took 300lbs of contaminated soil off the island. They threatened to unleash the anthrax on the public unless the island was decontaminated. The British government finally started cleaning the island in 1986. They sprayed formaldehyde, removed soil and deployed another flock of sheep.
The sheep survived, and since 2007, the island has been anthrax-free. Gruinard still gets very few visitors, because you can never be too safe.