The climax of The Golden Ass is when Lucius is transformed from donkey back to human form by the goddess Isis, in order to be initiated. Here’s what he says about the rites directly:
“Listen then, but believe; for what I tell you is the truth. I came to the boundary of death and after treading Proserpine’s threshold I returned having traversed all the elements; at midnight I saw the sun shining with brilliant light; I approached the gods below and the gods above face to face and worshipped them in their actual presence.”
The ending seems like a non sequitur, but tends to suggest that some or all of the fast-paced adventure narrative leading up to it, a series of ribald and violent scenes playing out lengthy journeys, magical transformations, exotic marriages, judicial proceedings, false deaths, and feasting, should be taken as an adventure tale retelling in some way the mysteries Apuleius claims to conceal.
Joseph and Aseneth, another Hellenistic tale (in this case a romance, rather than an adventure story), seems similarly to be entertainment concealing beneath it the deep secrets of mystery religion, with its angelic visitors, swarms of heavenly bees, and tales of sacred meals.
Two books make a genre, and what a fascinating genre this is! I’m sad no one is writing such novels today. At least, I’m unaware that such novels are being written. But then, maybe I’m just not initiated into the right mysteries.