Ōkunoshima is a small island belonging to Takehara City, Hiroshima Prefecture, and one of the Geyo Islands in the Seto Inland Sea. It’s also known as Rabbit Island and Poison Gas Island. Apart from some 900 rabbits, it has no permanent residents. The island can be accessed by ferry from Mihara and Tadano-Umi in Hiroshima Prefecture and from Ōmishima in Ehime Prefecture.

Many visitors come to the island just to see the rabbits and feed them carrot sticks, and to eat soft-serve ice cream at the Holiday Village Ōkunoshima hotel. However, the island is additionally interesting for its history as one of two Geyo Fortresses, finished in 1902, to defend against Russian ships during the Russo-Japanese war, and as site for the manufacture of poison gas by the Imperial Japanese Army from 1929 to 1945. You can visit the remains of the gun emplacements and searchlights, and there’s a museum documenting the misery wreaked by the poison gas. It’s a pleasant hike up to the top of the mountain where the best preserved remains are found. The electrical pylon on the mountain is the tallest in Japan.

The molars of Naumann’s elephant have been found in the waters around the island, indicating that the ancient Seto Inland Sea was once a plain and that the present island was then one of the hills. In the Middle Ages in 1129, Taira no Tadamori was authorised to pursue pirates in the area. Later, the descendants of the Murakami Suigun lived on the island. During the Shōwa period, Ōkunoshima was erased from maps to conceal the gas manufacturing taking place. At the end of the war, the Army dumped the gas and manufacturing equipment in the sea. When the Korean War broke out, the U.S. military seized the island and used the buildings on the island as ammunition depots, holding it until 1955.

The rabbits are thought to be the descendants of eight rabbits kept at a local elementary school that were released into the wild in 1971.