Sokushinbutsu (即身仏) were Buddhist monks or priests who caused their own deaths in a way that resulted in their mummification. This practice reportedly took place almost exclusively in northern Japan around Yamagata Prefecture. It is believed that many hundreds of monks tried, but only 24 such mummifications have been discovered to date.
Their diet was nuts and seeds for 1000 days, after that they only ate bark and roots while getting rid of body fat, After the 1000 days they drank a poisionous tea made from the sap of Urushi tree.
Finally, a self-mummifying monk would lock himself in a stone tomb barely larger than his body, where he would not move from the lotus position. His only connection to the outside world was an air tube and a bell. Each day he rang a bell to let those outside know that he was still alive.When the bell stopped ringing, the tube was removed and the tomb sealed. After the tomb was sealed, the other monks in the temple would wait another 1,000 days, and open the tomb to see if the mummification was successful.
If the monk was mummified he was instantly seen as Buddha and put on display. If the mummification wasnt successful then the monk wasn’t seen as one, yet still admired for his trying.