HIGH up in the Himalayas, tucked in a small ravine, lies a glacial lake that conceals a chilling secret.

When the ice thaws for one month of the year, hundreds of human skeletons are visible jutting out of the 2m-deep, cold mountain water. The bones, along with pieces of flesh and hair, have been preserved by the dry, frosty climate, yet they have clearly been there a long time. What happened to leave so many dead at the remote Roopkund Lake in Uttarakhand, India? For years, the eerie truth remained obscured. Locals nicknamed the spot, 5000m above sea level, the “Mystery Lake”, according to The Hindu, and strange myths sprang up about the ancient remains. When a British forest guard discovered the deathly site while hiking through the mountains during World War II, the military suspected they were Japanese soldiers sneaking through India, but the bodies had been there too long, Atlas Obscura reports. Others believed the skulls could have belonged to Kashmir warriors returning from the 1841 battle of Tibet, or to the royal party of King Raja Jasdhaval and his wife, Rani Balampa, after they were caught in a blizzard. Some said it looked like a mass suicide or epidemic. In 2004, scientists had a breakthrough. National Geographic journalists took 30 skeletons to the Centre for Cellular and Molecular Biology in Hyderabad for DNA tests. Samples were sent to the Radiocarbon Accelerator Unit of Oxford University, which revealed that the skeletons dated from as long ago as 850AD. They learned the remains had belonged to Indian pilgrims and their shorter local guides, with rings, spears and leather shoes found at the lake. They had all been killed by a fatal blow to the back of their heads by something hard and round, like a cricket ball. It appeared they had been caught in a severe hailstorm. Scientists believe as many as 600 bodies could still be buried in snow and ice by the lake, according to a Roopkund hiking website. Another mystery still lingers around the lonely spot. Skeletal remains and personal items are said to be disappearing from the site each year, stolen by hikers or blown away and obscured by snowdrifts. With little monitoring and maintenance of the distant location, its rich history may be lost to the ravages of time, and the secrets of hundreds more buried bodies hidden forever.