Baikal Ice Marathon, Siberia
Credit: Masaki Nakamura

Who: 165 runners

When:  March 1, 2015

Why it's unique: The race crosses Lake Biakal in Siberia, the largest and oldest lake on Earth (it's said to be 22 million years old and contain up to 20% of the world's surface water when unfrozen) and this race's goal is to raise awareness for clean water conservation and sustainable development of the area. The course is run entirely on ice so it's pancake flat, except for some ice rubble and snow but you're fighting wind chills that blast into you at negative 5 below. []