Okinoshima Island is a small uninhabited island located in Tateyama Bay in Tateyama City, Chiba Prefecture. Once completely surrounded by the sea, the island became connected to the mainland after the Great Kanto Earthquake of 1923, making it possible to reach Okinoshima on foot.
The island is a land-tied island and is now maintained as Okinoshima Park by Tateyama City. Its rich natural environment forms part of the Minamiboso Quasi-National Park, making it a fascinating destination for visitors interested in beaches, marine life, geology, and the natural landscapes of southern Chiba.
Okinoshima was originally a completely isolated island surrounded by the sea. However, the Great Kanto Earthquake caused the surrounding land to rise. Changes in ocean currents also encouraged sand to accumulate between the island and the mainland, eventually creating a natural land connection.
Today, visitors can walk from the mainland to the island, an unusual feature that makes Okinoshima especially attractive for sightseeing.
Rock formations and sedimentary layers dating back approximately 20 million years are exposed around Okinoshima. Walking around the island provides an opportunity to observe these geological formations and imagine the long history of the Earth’s natural environment.
The surrounding sea is also notable for its coral habitats. Okinoshima is known as part of the northern limit of coral distribution, where warm ocean currents allow coral and tropical marine life to survive farther north than might normally be expected.
Okinoshima benefits from the warm climate of southern Chiba and the influence of the Kuroshio Current. As a result, a variety of plants and animals associated with warmer regions can be found on and around the island.
The island’s vegetation includes evergreen trees such as camphor-like cinnamomum trees and Machilus trees, as well as subtropical plants including cycads, Chinese windmill palms, and coral trees.
In the surrounding waters, visitors may encounter colorful tropical fish such as damselfish and clownfish. Coral species, including brain corals and branching Acropora corals, can also be found in the area.
This combination of subtropical vegetation, coral, and marine life makes Okinoshima an appealing destination for visitors who want to experience a different side of Chiba’s natural environment.
The entire island is included within the natural environmental area of Minamiboso Quasi-National Park. The land is made available to Tateyama City through a free lease from Japan’s Ministry of Finance, allowing the island to be maintained as a public natural recreation area.
Okinoshima offers a variety of attractions within a relatively small area. Visitors can discover a historic shrine surrounded by vegetation, an unmanned lighthouse, and remains of underground tunnels built during the wartime period.
The combination of nature, religious heritage, and wartime history gives the island a distinctive atmosphere that is different from a typical beach destination.
Okinoshima Uga Daimyojin Shrine is a historic shrine traditionally said to have been founded in 1096. Its principal deity is Ukanomitama no Mikoto, a Shinto deity associated with food and agriculture.
A particularly impressive feature of the shrine grounds is a Machilus tree believed to be more than 300 years old. Surrounded by dense greenery, the ancient tree gives the shrine a peaceful and mysterious atmosphere.
The sandy beach next to Okinoshima is a popular destination for swimming and enjoying the sea. Water quality surveys conducted by Japan’s Ministry of the Environment have rated the water A or higher every year, reflecting the area’s relatively clean and clear coastal environment.
The cove on the northern side of the island is suitable for snorkeling and shallow-water exploration. Visitors can observe fish and coral in the clear coastal waters, while beachcombing along the shore is another enjoyable activity.
On the opposite side of the island, an area known as Ura-no-Hama is affected by stronger currents and is therefore not suitable for swimming. However, its rocky shoreline provides opportunities for exploring tide pools and enjoying shoreline activities.
Since 2017, visitors have also been encouraged to contribute to the Okinoshima Environmental Conservation Cooperation Fund. Contributions help support efforts to protect the island’s natural environment.
Okinoshima suffered extensive damage from Typhoon Faxai (Typhoon No. 15) in September 2019. Numerous trees were blown down, including the sacred tree at Uga Daimyojin Shrine, and the shrine’s torii gate was also destroyed.
Following the disaster, access to the island was temporarily restricted. The damage also affected tourism throughout the wider Minamiboso area.
Because restoration efforts initially focused on areas of Tateyama’s urban center, recovery on Okinoshima took time. However, local residents and nonprofit organizations supported cleanup activities and fundraising efforts, helping the island gradually recover.
Restoring the island’s natural environment is a long-term process, and continued conservation efforts are important for protecting Okinoshima for future visitors.
From the East Exit of Tateyama Station on the JR Uchibo Line, take the Tateyama Nitto Bus bound for Tateyama Kōkūtai. Get off at the final stop and walk for approximately 25 minutes.
Alternatively, take a JR Bus Kanto service toward the Suzaki area, get off at the Miyagi bus stop, and walk for approximately 30 minutes.
Rental bicycles are also available around Tateyama Station, providing another convenient option for exploring the coastal area.
Okinoshima is approximately 11 km from the Tomiura Interchange on the Futtsu-Tateyama Road. Visitors traveling by car can use the free parking area with space for approximately 500 vehicles.
Okinoshima Island is a unique destination where visitors can walk from the mainland onto an uninhabited island and experience a remarkable combination of nature, geology, history, and marine life.
The island’s transformation from an offshore island into a land-tied island after the 1923 earthquake is itself an interesting part of its history. Meanwhile, its 20-million-year-old geological formations, coral habitats, subtropical vegetation, and tropical fish make it an appealing place for nature lovers.
Visitors can also discover Okinoshima Uga Daimyojin Shrine, an ancient tree, an unmanned lighthouse, and wartime underground remains while exploring the island. During the beach season, the nearby sandy beach provides opportunities for swimming, snorkeling, and beachcombing.
For travelers exploring Tateyama and the southern Boso Peninsula, Okinoshima offers a memorable way to experience the natural and cultural diversity of coastal Chiba.