Mount Teide, Canary Islands, Spain

Rising to 24,600 feet from its base on the ocean floor, Mount Teide in the Canary Islands is the third highest volcano in the world and Spain's most visited natural wonder.

While its last violent eruption was more than 150,000 years ago, Mount Teide has featured smaller events within the past 300 years, with the last occurring in 1909. Scientists estimate that should the volcano erupt in the future, it will likely be a cataclysmic event; owing to a structure similar to its deadly neighbors, Mount Vesuvius and Mount Etna.