Tombolo is a shingle isthmus that connects Dogashima with the Sanshiro Islands at low tide. Tombolo is named after the Italian word Italian: [[tombolo]], meaning 'pillow' or 'cushion', which refers to a deposition landform by which an island becomes attached to the mainland by a narrow piece of land such as a spit or bar.[1]
Tombolo begins at Hamase Beach on Dogashima and extends to Elephant Island and Nakano Island of the Sanshiro Islands.[2] A small canal cuts off Tombolo between Elephant and Nakano Island.[2] The tombolo is 250 meters long and 30 meters across at low tide between March and September.[3] Rather than being sandy, the tombolo is stoney, with the rocks often covered by seaweed and slippery to walk on.[3]