The Cave allegory Plato spoke about was not attributed to a "cave" in the literal sense, but rather to an inner "cave" that resides in all individuals. He referenced rows of people at different levels; the first only knows a wall with shadows. On the elevation behind the first row, they are aware of the existence of other and the various objects they carry.
All of the people within the cave, both those facing the wall and those on the elevated wall have one thing in common; they are all "prisoners". Some have knowledge of objects and materials and of others existence, but they are held captive from the "true" outside world.
When the prisoner is released into the "true" world he is forced to face reality of the existence of water, sunlight, wind, flowers, and not only the existence of others, but his existence in this new world. He is thrown into the new reality and forced to learn on his own, such as the use of his senses. How sunlight affects his sight, the tough of water on his skin, the smell of fragrant flowers, and the tastes of new fruits in his mouth.
When the prisoner is returned to the cave he is seen as an outcast and is ridiculed for not having the capability to participate in the "games" that he once enjoyed. Plato suggests that once one has been enlightened, you are viewed as a threat to the other prisoners" way of life. In many cases, seen today, different views are criticized. And the bearers of such views and ideas are tortured or even killed.
The cave symbolizes those who are afraid of the unfamiliar and see only one way of doing things. Anyone or anything that is different from what one believes to be true is considered wrong. This is seen today in racism, sexism, different religious beliefs, and even in various cultures. It is the individual who dares to embark on the quest for knowledge, by education, who truly breaks free from the chains of an oppressive society.