A boy sent to Death itself bargains for the one secret no living teacher will tell him — what waits beyond dying.
Dialogues in this Upanishad
Nachiketa and the Lord of Death — Sent to Death by his father's careless word, a boy waits three days at Yama's door — then spends his last boon on the secret of dying.
The Chariot of the Self — Yama's great image: you are the rider, the body your chariot, the intellect the driver, the mind the reins, the senses the horses.