With an impressive age of 25 million years, Lake Baikal in southeastern Siberia is the oldest lake in the world; with depths reaching nearly 5,400 feet, it is also the deepest lake on the planet. In fact, it contains 20 percent of Earth’s total unfrozen freshwater reserve. But beyond its impressive stats, it is a marvel of nature and beauty. Known as the "Galapagos of Russia," Lake Baikal is one of the most biodiverse places anywhere, thanks to its age and isolation. It plays host to over 1,340 species of animal (745 endemic) and 570 species of plant (150 endemic). The area surrounding the lake is no less spectacular and includes mountains, boreal forests, tundra, lakes, islands and steppes; according to UNESCO, which includes the region in its World Heritage List, the area is “exceptionally picturesque.” Even just a sliver of the lake when frozen, as pictured here, hints at its secrets and allure.