Of all the fates that can befall a person, being mummified while alive sounds like one of the worst – but for some Buddhist monks from the Japanese Shingon sect in Yamagata prefecture, living mummification wasn’t something to be scared of. In fact, it was pretty much the best thing a person could do. This is why, between 1081 and 1903, as many as 30 members of the sect decided to do it. They mummified themselves to death, and became sokushinbutsu, or “a Buddha in this very body.”

“The process of self-mummification is long and arduous, taking at minimum three years of preparation before death,” explained Davey Young in Atlas Obscura. “Central to this preparation is a diet called mokujikigyō, literally ‘tree-eating training.’”

The name is appropriate: for a thousand days, the monks would subsist on only pine needles, nuts, roots, buds from trees, and in some cases even stones, all foraged from the mountain where they lived alone. If that doesn’t sound very filling, well, that’s the point. The monks believed this extreme diet would “toughen the spirit” and “distance [them] from the common human world,” writes Young – but from a more practical point of view, it would starve them of calories and nutrients, eliminating all that fat and moisture that encourages decay after death.

After completing this three-ish-year regimen, the monks were theoretically ready to die – or, as they saw it, entering nyūjō, a state of meditation so deep that it is essentially a kind of suspended animation. However, you only get one chance at self-mummification, so you want to do it right – which is why some monks spent as long as ten or eleven years following this strict, lonely, mountain life. After their final cycle, they would cut out food altogether, and drink only salt water for the last hundred days of their life.

It must have been a difficult balance to strike for the old and starving monks. Attempt to enter nyūjō too soon, and you may not be dried out enough to achieve mummification – that would mean complete failure, since the monk’s body would be exhumed and examined for signs of rot, and if it was found then it would simply be buried like any normal non-Buddha corpse. However, take too long in your preparation, and you risk accidentally dying from starvation or illness – surviving for 100 days on just water is basically a superhuman feat on its own. Several stone monuments ended up being left in memory of those would-be sokushinbutsu who didn’t quite make it.

But for the lucky monks who survived long enough to feel their bodies begin to die, the next step was a bit nicer: a cup of tea and a sit down. Specifically, the tea was made from Toxicodendron verniculum tree bark, which contains the same toxin found in poison ivy, and the sit down was in a pine box at the bottom of a three-meter-deep (about 10 feet deep) hole in the ground. The box would then be buried in a layer of charcoal, with just a small bamboo straw in the lid for air, and the monk would be left to meditate until death.

A thousand days later, assuming no rot had set in, the monk would be declared a sokushinbutsu and enshrined. Even today, in certain Buddhist temples, you can see the mummified remains of those monks who, according to tradition, became so enlightened that they cheat-coded death. They won’t be seen again on this mortal realm for approximately 5.67 million years, the lore says, when they will return to guide the deserving into nirvana.

While it may seem gruesome, the Shingon sect is far from the only religious group to believe in immortality through bodily integrity. In fact, one of the reasons cremations were verboten for so long in Europe was that Christians thought it would stop the deceased from being resurrected on judgment day.

Besides, perhaps the sokushinbutsu are onto something. Maybe they really are stuck in a state of perpetual meditation, just waiting to wake up in 6 million years.

Guess we’ll just have to wait and find out.