When I visited the Tenerife island I decided to check out El Teide - the volcano. It's actually 3718 meters above the sea level, but if you measure the height from the ocean bottom, it's 7500 meters, which makes Tenerife the tenth highest island in the world!
El Teide
The best way to get up there is taking the cableway, and it's totally worth it (it doesn't take you to the summit, though - to get there you have to have a special permit, which, unfortunately I didn't have). The views from the top are just astonishing!
View from the top
What's interesting, the volcano is still active and you can actually feel the warm air coming from underground if you find the right spot :D
Solid lava can be seen all around the volcano