Okunoshima is a small Japanese island in the Inland Sea of Japan.The island is also referred to as "Rabbit Island" because of the numerous wild rabbits that occupy it.
Due to it's isolation, the Japanese chose Okunoshima as the location to build a chemical munitions plant from 1927-1929. This was expressly forbidden in the Geneva Protocol of 1925 so the plant was kept a secret.
The chemical weapon facility produced tons and tons of mustard and tear gas. At the end of the war, the gas was disposed of by dumping, burning or burying it.
After WWII, in a effort to rehabilitate the island, many rabbits were set loose there. It is forbidden to hunt these animals, and dogs and cats are not allowed on the island.
The island also plays host to the Poison Gas Museum, which tells Okunoshima's dangerous history.