The cave was designated as a National Natural Monument of Japan in 1935.
The ceiling opening is approximately 10 meters in diameter.
The cave is formed from a type of white volcanic tuff that is highly susceptible to coastal erosion.
The illumination effect inside the cave is known as 'Blue Grotto' due to the reflection of light on the seafloor.
The Dougashima Sea Cave Skylight, known locally as Tensodo, is a sea-eroded grotto formed by wave action on volcanic tuff cliffs. The site's primary feature is a circular opening in the cave ceiling, created by the collapse of the rock roof. Sunlight filters through this skylight to illuminate the turquoise water below, creating a distinct visual effect. Visitors typically access the cave interior via boat tours departing from the adjacent bay. The cave is part of the Izu Peninsula UNESCO Global Geopark. The rock layers visible within the grotto provide evidence of ancient submarine volcanic activity.
Inside the tour boat directly beneath the skylight opening.
Bring a polarizing filter for your camera to better capture the water's transparency through the skylight.
Check the tide levels, as very high tides may cause boat tours to be cancelled for safety.
Wear a light jacket, as the cave interior is significantly cooler than the exterior temperature.
Do not attempt to swim into the cave or access the cliffs independently, as the currents are strong and the rock is unstable.
Tours are subject to cancellation during rough sea conditions or strong wind warnings.
Remain seated inside the excursion boats at all times for safety and stability.
