Lake Baikal is an ancient, massive lake in the mountainous Russian region of Siberia, north of the Mongolian border. Considered the deepest lake in the world, it’s circled by a network of hiking paths called the Great Baikal Trail. The village of Listvyanka, on its western shoreline, is a popular starting point for summertime wildlife-spotting tours, plus wintertime ice-skating and dog sledding.