You’ve probably never heard of Roopkund, an extremely high glacial lake in India’s northern state of Uttarakhand. If you went there to visit today, by clambering nearly 4,900 meters (about 16,000 feet) right up into the Himalayas, you’d find a shallow, green-tinted lake probably surrounded by snow, and – apart from fellow trekkers – you’d be in an area that’s essentially uninhabited.

As reported by the ever-marvelous Atlas Obscura, however, this lake is also chock full of human skeletons. Not just a handful, mind you, but a massive collection of them. Although for eight months of the year the lake is iced over, when it melts during the warmer months, the bones just pop up to greet whomever is walking past them at the time.

What the hell, you may wonder, happened here? That was indeed what a British forest guard in the middle of the Second World War asked; he stumbled across the remains in 1942, and initially assumed that these were the remnants of Japanese soldiers who had died trying to sneak into India – at the time, part of the British Empire.

Until the year 2004, it was unclear where the roughly 200 skeletons had come from. Although some were still wearing jewelry, there wasn’t anything with them that could be used as definitive sources of identification, so hypotheses abounded as to who they were and what killed them. Were they all killed on site by a natural disaster or a disease, or were they slaughtered somewhere else and dumped in the lake?

Shortly after the turn of the new millennium, though, an expedition to the site and subsequent DNA analysis revealed that they were all from around 850 CE.

Skeletal remains found at Roopkund Lake. Schwiki/Wikimedia Commons; CC BY-SA 4.0

They were two groups, not one: the first being a family of some kind, and the second being a more genetically disparate and vertically challenged group, perhaps guides or those carrying their stuff. It wasn’t entirely clear where they were heading, but it was perhaps on a pilgrimage of some sort.

Turns out that all the bodies had the same wounds: massive trauma to their heads and shoulders. That led experts to reason that they were all killed by a sudden, massive hailstorm, not unlike the one that killed two animals at a zoo in Colorado this very month.

According to The Weather Channel, fatalities from large hail are rare, but they do happen. The National Oceanic and Atmospheric Administration estimate that around 24 people per annum are injured in this way in the US alone. India currently holds the record for the deadliest hailstorm, which killed 246 people on April 30, 1888.

As it so happens, the deaths of these people are hinted at in an otherwise more fantastical legend about vengeful deities and monarchs, passed down for generations by those living in the region.

According to The Daily Beast, as the area is difficult to get to and examine due to its extreme topography and frigid conditions, there could be twice the human remains there than expeditions have currently uncovered. This also means that the area is difficult to protect, with the Indian Express reporting that many of the bones have been extracted by thieving trekkers.

If you aren’t a thief and can’t make it to the lake, you can visit the Anthropological Survey of India Museum in Dehradun, where some of the remains are held. As of 2009, authorities had plans to turn the lake into an eco-tourist destination, in order to better protect the bones and to educate the public about their story.

[H/T: AtlasObscura]