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Setonaikai NP, Wakayama
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A 2024 excavation exposed a 5.4 m gun seat at Tomogashima’s largest battery, ringed by 52 anchor holes. It held a 28 cm howitzer; the battery’s 8 guns could fire in every direction.
Tracks recorded in 1954 and a carcass found in 1955 made Tomogashima one of Honshu’s latest documented sites for the Japanese river otter. Japan’s environment ministry listed the species as extinct in 2012.
Built in 1872, Tomogashima’s Brunton-designed lighthouse is among Japan’s earliest Western-style beacons. In 1890, the Army shifted it about 25 m to make room for a gun battery.
On Torajima lies Juhon Cave, the first of the 28 Katsuragi Shugendo scripture mounds. The pilgrimage tradition also says En no Gyōja began his mountain training on Tomogashima.
Across the strait in Kada, the local dish nia-i began as a fishers’ boat meal: fresh fish cooked with only tamari soy and sake. Eaten since the late Edo period, it is now recognized as a 100-year food.
Tomogashima became a fortress garrisoned by about 600 soldiers and stayed closed to civilians until World War II ended. During wartime, detailed maps even erased the islands from view.
The wider Yura Fortress, including Tomogashima’s batteries, was put on emergency alert during the Russo-Japanese War—but never used in actual combat, even during the Pacific War.
The waters around Tomogashima are important spawning and wintering grounds for red sea bream. Kada fishers still catch them by traditional single-hook line fishing, which helps avoid damaging the fish.
Shinja Pond is a freshwater relic lake on a sea-surrounded island. Researchers have identified layers interpreted as tsunami deposits in its sediment, which may preserve clues to past coastal inundations.
Tomogashima’s Shinja Pond wetland is a prefectural natural monument. It supports northern-limit communities of the plants Hitomoto-susuki and Tetsu-hoshida, as well as a large stand of Hangeshō.
Tomogashima’s sandstone contains ammonite fossils, and some of its thick slabs were quarried for Wakayama Castle’s stone walls. Tool marks from the old quarrying can still be seen on the islands.
A local legend says the storm-tossed Empress Jingū followed a floating boat covering, called a toma, to safety here. The island was supposedly named Toma-ga-shima, later becoming Tomogashima.
The 135°E meridian used to define Japan Standard Time crosses Okinoshima. Tomogashima marks the southernmost place in Japan touched by that line, commemorated at the island’s meridian plaza.
In the Edo period, Tomogashima served as a horse-breeding ground for the Kishu Domain—a pastoral chapter in the islands’ story before they became a heavily fortified military outpost.
Tomogashima inspired Hitogashima, the fictional island in the manga and anime Summer Time Rendering. Its real coves and old fortifications also have a place on a modern pop-culture map.
