Russia"s Lake Baikal is a record-holding wonder: It"s the world"s oldest (25 million years), deepest (over 5,000 feet in some parts), and largest freshwater lake (more than 20 percent of the Earth"s fresh surface water by volume). Baikal lies in the deepest continental rift on Earth, and because the rift is geologically active, the tectonic plates continue to move farther apart.