The world’s tallest mountains, including Mount Everest and K2, are associated with great mountaineering feats, a love of nature, and tales of adventure. These 8000-meter peaks also hold a dark side for climbers, however, and there are just as many stories of hardship, defeat, and death on the summits. Among these tales are a surprising number of accounts of the strange, ghostly, and supernatural.

To begin with, the atmosphere on the tallest peaks can be somewhat grim. Death is a constant possibility to be reckoned with for climbers on the highest peaks of the Himalayas and the Karakoram range, which spans Pakistan, India, and China. Over 220 people have died climbing Everest, and due to the impossibility of retrieving the fallen, the majority of bodies are left frozen on the slopes indefinitely, turning the mountains into a high-altitude cemetery.

Some of the bodies remain visible, lying close enough to the main routes that climbers are obliged to step over them. The colorful gear worn by the dead has earned Everest’s Northeast Ridge route the nickname “Rainbow Valley.” Everest, however, is not the deadliest 8000-er in terms of percentages. Since the first successful ascent of K2 in 1954, over 25 percent of those who have attempted the summit have died, while Annapurna I’s death toll is closer to 33 percent. It’s no wonder that the area between around 8000 meters and the tops of these mountains is ominously referred to as the “Death Zone.”

Given this macabre climate, it’s inevitable that some weird stories have emerged. Some of these spooky tales are informed by the mountains’ cultural and spiritual significance, and some can be explained by science, while others remain inexplicable.

The Sherpas, without whose help so many ascents of Himalayan mountains would be impossible, view the Himalayas as both the embodiment and the realm of gods. Some feel that disrespect for their sacred mountain has led to both bad karma and to restless spirits. In May 2004, Pemba Dorji Sherpa was climbing Everest, a trip during which he earned a disputed claim to the world’s fastest ascent, when he encountered what he described as black shapes near the summit. Pemba says that the shapes were the ghosts of climbers who died on the mountain, and that as the shapes approached him they held out their hands, begging for something to eat. Pemba and other Sherpas believe the ghosts will continue to haunt the mountain until a proper funeral rite can be performed for their souls.

The scientifically minded feel that ghostly sightings above 8000 meters have a much more logical explanation. The detrimental effects of time spent in the Death Zone are well-known. At high altitude, temperatures far below freezing inflict frostbite, sleep becomes difficult, and reflected light causes snow-blindness. Perhaps worst of all, though, the lack of atmospheric pressure and attendant low oxygen concentration (about 30 percent of that at sea level) can cause altitude sickness and High Altitude Cerebral Edema, or HACE. In the latter condition, the brain swells, leading to hampered speech and mental function, poor decision-making, impaired coordination, hallucinations, and loss of touch with reality.

Altitude’s effects on the brain can explain a particularly haunting moment described in Jon Krakauer’s Into Thin Air, a first-person retelling of a 1996 Everest expedition during which a severe storm killed eight climbers on the mountain and stranded several others. The incident is considered one of the worst-ever mountaineering disasters. Krakauer, descending in the midst of the mounting storm, at one point thought he encountered his teammate Andy Harris, only to discover later that he had seen an entirely different person, and that Harris had died up on the mountain.

Low oxygen and other physical stresses can also account for a common phenomenon in which mountaineers report the sense of an additional, phantom person. Dougal Haston and Doug Scott, members of a 1975 British expedition up Everest, describe a horrific night spent just below the summit with no food and problems with their oxygen supply. The men are said to have sensed a third climber with them in their snow hole, a comforting presence that talked them through their ordeal. Climber Hermann Buhl experienced something similar on his first-ever ascent of Nanga Parbat in 1953, as did Joe Simpson, whose ordeal escaping death in the Andes is described in Touching the Void.

British climber Frank Smythe, who attempted Everest several times in the 1930s, may have the most colorful story, however. He describes encountering two presences, the first being a benign one that seemed so real he offered it some of his mint cake. Later, he encountered strange hovering objects, one of which had "what looked like squat, underdeveloped wings, whilst the other had a beak-like protuberance like the spout of a teakettle. They distinctly pulsated … as though they possessed some horrible quality of life."

Michael Shermer’s book The Believing Brain reports that the so-called sensed-presence effect (referred to elsewhere as “Feelings of Presence,” or FOPs) is common to people under physical and mental duress, including mountain climbers, polar explorers, endurance athletes, and isolated sailors. An experiment conducted by a Swiss team in 2014 and reported in Current Biology seems to confirm this. Researchers managed to induce in volunteers the experience of nearby ghostly presences by creating a disconnect in motor-sensory signals received by the brain, causing the brain’s sense of the body in space to malfunction. Researchers suggest that FOPs, or ghosts, may be an illusion created by the mind when it temporarily loses track of the body’s location due to mental illness, stress, or extreme physical exertion or duress.

Not all mountaineering ghost stories can be explained away so easily, however. Jennifer Jordan’s book Savage Summit, which details the lives and feats of the first five women to climb K2, also presents a few accounts that would not be out of place in a book of ghost stories. Wanda Rutkiewicz, an accomplished Polish mountaineer who in 1986 became the first woman ever to climb K2, survived the descent and went on to climb several other 8000-foot mountains before dying in her bid to climb Kanchenjunga in 1992. After Rutkiewicz’s death, Jordan writes, her friend Ewa Matuszewska was awoken in the middle of the night by a telephone call, and upon answering heard Rutkiewicz’s voice on the other end of the line. Delighted to hear her friend’s voice, Matuszewska pleaded, “We are all in despair. Where are you?”

The voice responded,“I am cold, I am very cold, but don’t cry. Everything will be fine.”

“But why aren’t you coming back?” Matuszewska persisted.

“I cannot now,” Wanda’s voice said, before the phone went dead.

Equally chilling is a story from Jordan’s book involving Julie Tullis, a British climber and the third woman to summit K2. Tullis’s accomplishment took place in July of 1986. The months surrounding her climb saw 13 deaths on K2, which came to be known as the Black Summer. During her descent with her partner Kurt Diemberger, Tullis suffered a bad fall, severe frostbite to one hand, and blurred vision likely stemming from HACE. She died while trapped at Camp IV with several other climbers, and her body was left on the mountain.

Years later, in 1992, Thor Kieser and Scott Fisher, members of an American-Russian team, were jolted out of an unusual quiet at base camp by the sound of a voice coming over the communications radio. “Camp IV to Base Camp, do you read, over?” the voice said. Both Kieser and Fisher knew that no one was on the mountain at that time. And the voice was that of a British woman.