In the Republic, Socrates describes prisoners chained in a cave, seeing only shadows cast on the wall. One is freed, turned around, dragged up into the light, and at last sees the sun; returning, he is mocked. The allegory images education as a turning of the soul and philosophy as an ascent and return.
Allegory of the cave
Plato’s image of prisoners who take shadows for reality until one is freed and climbs to the sun.
Also: Plato’s cave