The Duat is the best documented afterlife in the ancient world because the Egyptians drew it on the walls. The Amduat, the Book of Gates and the Book of Caverns are compositions painted in New Kingdom royal tombs, and they are structured as an itinerary: twelve hours of the night, each with its own gate, its own guardians, its own inhabitants, and text naming them. Knowing the names is the point, because a gate opens for someone who can address its keeper correctly.
What the sun does there is the organising event. Ra enters the west, travels the twelve hours, unites with Osiris at the deepest point, and is reborn in the east at dawn. The dead king travels with him. Every sunrise is therefore a demonstration that the passage works, which is a considerably stronger argument for an afterlife than assertion.
The texts also record a social change. The Pyramid Texts of the Old Kingdom were for the king. The Coffin Texts of the Middle Kingdom appear on the coffins of officials. The Book of the Dead of the New Kingdom could be bought as a papyrus, sometimes with blanks left for the purchaser's name. Over roughly a thousand years the passage through the Duat went from a royal prerogative to something available to anyone who could pay a scribe.