The island's red brick buildings were constructed using a specific method called 'French stacking' (French Bond), making them rare examples of Meiji-era industrial architecture.
Sarushima was used by the Imperial Japanese Army as a coastal defense fortress until the end of World War II.
The island served as a filming location for the 1970s tokusatsu series Kamen Rider, leading to its local nickname as 'Kamen Rider Island'.
The rock layers on the island are primarily composed of Neogene tuff, which has been sculpted by marine erosion into unique formations.
During the Edo period, the island was part of the 'Tokyo Bay Fortress' project aimed at deterring American and European warships.
The island is uninhabited and has been designated as a Prefectural Natural Park to preserve its unique ecosystem and historical structures.
Sarushima is the only natural island in Tokyo Bay, located approximately 1.7 kilometers off the coast of Yokosuka. The island served as a critical defensive outpost during the late Tokugawa Shogunate and Meiji era, housing a sea fort designed to protect Edo from foreign naval threats. Its most distinctive features are the red brick tunnels and barracks constructed using the 'French-style' masonry technique, which remain largely intact. The island was declared a national historic site in 2015. Visitors can explore a network of subterranean ammunition depots, tunnels, and gun battery emplacements built into the island's rock face. Nature has gradually reclaimed parts of the fort, creating a unique aesthetic where moss-covered brick walls contrast with lush greenery.
The entrance to the primary brick tunnel, where the depth of the masonry and the light contrast create a dramatic frame.
Wear sturdy walking shoes as the island trails and tunnels can be uneven, damp, and slippery.
Bring mosquito repellent, as the island's wooded areas and tunnels can be dense with insects during the warmer months.
Carry all trash off the island with you, as there are no public waste disposal facilities available for visitors.
Do not attempt to swim in areas not designated as public beaches, as currents around the island can be dangerous.
Operations are weather-dependent; ferry services may be canceled during high winds or rough seas. The island is accessible year-round but ferry frequency reduces significantly during the winter months.
Do not climb on the historical brick walls or enter fenced-off restricted areas; stay on marked paths to protect the site's structural integrity.
