Explain how is "Diving into the Wreck clearly an allegory"?
Are you referencing Adrienne Rich's poem, "Diving Into the Wreck?" If so, I can help. An allegory is basically a story about one thing which actually symbolizes something else. Myths, which Rich speaks about in her poem, are a type of allegory. For instance, the myth of Persephone descending into the underworld is used to explain the seasons.
One a literal level, the poem describes a scuba diver exploring a sunken wreck of a ship. But allegorically, it means something very different. The "wreck" can be read as an emotional or psychological trauma, something which has been buried, or "sunken" in one's psyche for a very long time. By exploring this past trauma, the speaker comes to understand herself and her past much more completely than by simply reading the "myth" of her life.