He was an adult male, estimated to have been between roughly 35 and 45 years old when he died.

He was physically robust — compact and muscular in the way that a life of sustained physical demand builds a body.

And he had made it, somehow, more than a thousand feet into the dark interior of a cold, muddy, extremely difficult cave system at more than ten thousand feet above sea level.

This is the story of who he was.

Of how he got there.

Of what the science eventually learned from his bones and from the cave itself.

And of the one question that science, for all its power, still cannot answer: why.

A Cave That Fights Back

Hourglass Cave is not a tourist attraction.

It never will be.

The cave sits in the Colorado Rockies, in Eagle County, at an elevation that most sea-level residents would need time to acclimate to before doing anything more strenuous than walking slowly.

Above 10,000 feet, the air contains roughly a third less oxygen than at sea level.

Physical exertion that would be unremarkable at lower elevation becomes demanding at high altitude, and sustained exertion can produce headaches, nausea, and poor judgment even in people who are generally fit.

The cave entrance does not announce itself dramatically.