|photo taken by soviet authorities at the abandoned camp|
The Dyatlov Pass Incident is the creepy and true mystery of nine experienced Russian cross-country skiers, led by Igor Dyatlov, in 1959.
All that is known is during the night all nine suddenly fled their tent, cutting it open from the inside, and raced out into the sub-zero temps without coats or boots, most in their underwear, some even barefoot or with a single sock or boot. They ran downhill toward a wooded area some 1.5 kilometers away. Most died of hypothermia; though the corpses showed no signs of struggle, two victims had fractured skulls, two had broken ribs, and one was missing her tongue. Oh, and there were traces of radiation on their clothing.
Don't get too creeped out though. You can find many excellent, and logical theories online (just google it, if you are interested) but one I just do not buy is paradoxical undressing, or shedding your clothes when suffering from hypothermia. They built a fire in the woods, and as they died, the survivors took clothing from the dead, which isn't exactly 'paradoxical undressing' behavior.
Not that I think it was aliens; it was probably just a radioactive yeti.