Boudhanath is a powerplace where Padma Sambhava concealed treasures (termas) for rediscovery by accomplished yogins. The most important revelation to be discovered here was the Longchen Nyingthik, a cycle of dzokchen instructions, revealed by Rikzin Jigme Lingpa, a Tibetan yogin in the 18th century and an emanation of Guru Rinpoche Padma Sambhava. The revelation actually occured to Jigme Lingpa in a vision during his meditation in Central Tibet. In a heightened state of devotion and awareness of universal suffering, he had a vision of a white snow-lioness who took him on her back to the Great Stupa. On the eastern side of the Stupa he encountered a Wisdom Dakini, who handed him a sealed wooden casket with the advice that therein was the Heart Treasure of Samantabhadra, the Symbol of Rikzin Padma’s Infinite Mind, and the Dakini’s great secret treasure. Opening the casket he found five scrolls of yellow parchment and seven small crystals. He unrolled the largest of the parchment scrolls and discovered an outline of a stupa covered with indecipherable dakini script. He began to roll it up again but the dakini script suddenly dissolved and reformed as the Tibetan script of a text treating Mahakarunika. The Great Compassionate Buddha, like an image in a mirror. Thus The Great Stupa was a primary source of the Longchen Nyingthik, a complete dzokchen path to enlightenment.
Boudhanath: The Great Stupa by Keith Dowman