Jamieson, Fausset and Brown on Deuteronomy 34:6

6. he buried him--or, "he was buried in a valley," that is, a ravine or gorge of the Pisgah. Some think that he entered a cave and there died, being, according to an ancient tradition of Jews and Christians, buried by angels (Jude 9; Nu 21:20).

no man knoweth of his sepulchre unto this day--This concealment seems to have been owing to a special and wise arrangement of Providence, to prevent its being ranked among "holy places," and made the resort of superstitious pilgrims or idolatrous veneration, in after ages.