Naropa harnessed the power of his breath to keep himself from freezing to death. The practice became known as Tummo, the Tibetan word for “inner fire.” Tummo was dangerous. If used incorrectly, it could elicit intense surges of energy, which could cause serious mental harm. For that reason, it was reserved only for advanced monks and stayed in the Himalayas, locked up in the Tibetan monasteries for the next thousand years.
