The island is home to a thriving population of sea slugs and northern-most coral reefs due to the warm Kuroshio Current.
During World War II, the Imperial Japanese Navy used the island as a bunker and ammunition storage site.
The island was originally detached from the mainland but became connected due to reclaimed land and sediment accumulation.
The interior forest contains dense patches of tabunoki (Machilus thunbergii) trees.
The beach is characterized by abundant sea glass and fossil-rich sediment layers.
It is a popular location for 'beachcombing' due to the specific tidal currents that deposit diverse oceanic materials.
Okinoshima Park is a tidal island in Tateyama Bay connected to the mainland by a narrow sandbar, making it accessible by foot during low tide. The island features a pristine beach and an intertidal zone rich in marine biodiversity, including coral and tropical fish species. It served as a strategic military outpost during World War II, evidenced by preserved cave ruins and tunnels. The island is part of the Minamiboso Quasi-National Park and maintains a largely undeveloped, natural coastal ecosystem. Visitors can explore a forest trail that loops around the interior of the island. The sandbar transition makes it a unique geographic formation within Chiba Prefecture.
The sandbar path during low tide looking toward the island's entrance.
Check local tide tables before visiting to ensure the sandbar is traversable.
Wear water shoes if you intend to explore the rock pools and coral areas.
Bring a flashlight if you plan to enter the accessible wartime cave ruins.
Attempting to cross the sandbar during high tide or high-wind conditions; touching sea creatures in the tide pools.
Take all trash with you as there are no public waste bins; do not remove coral or marine life from the tide pools.
