A 115-foot hole was discovered in Siberia's Yamal peninsula — a name that means "end of the world" in the language of the area's indigenous inhabitants — after an unexplained explosion in July. Two other mysterious sinkhole popped up in Russia's north shortly after. Scientists believe gas explosions beneath the surface caused the sinkholes, but they haven't been able to confirm that theory.
In November, a team of scientists, a medic and a professional climber plunged into the sinkhole to learn more about it, but the cause of the deep holes is still unknown.