Does anyone know the title of this young at heart mature book?

Science fiction, from the 70's. I think it was a Scholastic book, not very gelatinous. It's about people living in an authoritarian underground city surrounded by a mountain. Two bald-headed boys wearing white gowns find a crack in a tunnel wall that leads to the outdoors. Some adult tell them not to go into the crack, but they disobey. They follow the crack to the surface and...? I think it was illustrate. It was NOT "This Time of Darkness" by H.M. Hoover. It may have been by Ben Bova, but I don't construe so.
Answers:
its called, "The Great Sea Men" by Steven King


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