Sarushima

Sarushima, literally “Monkey Island,” is a small natural island in Tokyo Bay off the coast of Yokosuka. It is notable as the only natural island of significant size in the bay and is managed as a public recreation area and historical site.

Visitors follow short walking circuits around the island to see Meiji- and early-20th-century coastal-defence works, exposed concrete gun emplacements, and ruined magazines. A small beach and raised viewing platforms give sheltered swimming and broad sea views in summer.

Coastal batteries and support structures were built and upgraded on the island from the late 19th century into the 20th century to defend Tokyo Bay; many of those fortifications remain as ruins. The island’s tunnels and chambers were part of these military installations and are now part of the visitor trail.

Sarushima lies off the Miura Peninsula near Yokosuka and is reached by a short ferry ride from the mainland; the trip typically takes around 10 minutes from the port.

• Ferry access: Served by a regular passenger ferry from Yokosuka that takes about 10 minutes, with more frequent services in summer.
• Distinctive feature: The only large natural island still extant in Tokyo Bay, with publicly accessible fortification ruins and walking paths.

What to See #

• Battery ruins: Concrete and stone gun emplacements and ammunition stores are visible around the island; many date from late 19th and early 20th century coastal-defence upgrades.
• Underground tunnels: A short network of tunneled passages and chambers runs beneath the island, originally built to link defensive positions and now accessible to visitors along marked routes.
• Beach and viewpoint: A small sandy bay and an elevated viewing platform provide swimming access in season and panoramic views across Tokyo Bay toward Yokosuka and the Miura Peninsula.