Photo by @shonephoto (Robbie Shone) - The Monte Corona (Crown Mountain) lava tube system on the Canary island of Lanzarote must rank as one of the world’s classic lava tubes. This lava tube was formed during the eruptions of Monte Corona volcano some 3,000 - 4,500 years ago. Pictured here, an explorer walks by one of the lava tubes classic features running along the lefthand side of the tunnel. Known as a bench, it's effectively a 'tide-mark' left when the lava surface was slightly higher. Where the lava touched the wall it cooled and formed a semi-solid lining that can be anything from an inch to a foot or more thick. When the level dropped, the solidified lining remained to form a bench.