Can't remember the name but it's a novel I read in the 80s, in which two kids from an underground society go through a old mechanism that transfers them to the above ground domed society.
Could it be City Under Ground (1964) by Suzanne Martel? It's about two kids, and later a third who manage to find their way out of their post nuclear, technologically advanced human society back onto the Earth.
A community, known as Surreal, has developed from a small band of survivors who retreated at the time of the Great Destruction, In the following centuries a civilization which is technologically, intellectually, and socially extremely advanced has been developed. Despite the widespread belief that Surreal is the only remaining society, it suddenly develops that there is another, apparently hostile, group of people which is draining off the city's all-important electricity. Meanwhile a 12-year-old boy, Luke P 9 becomes so curious about the outer world that he overcomes his fears of the poisonous gases on earth, against which the citizens of Surreal are continually warned.
Was it a novel meant for young adults? Could it be "This Time of Darkness" by H. M. Hoover?
Eleven-year-old Amy lives in a decaying underground city. Ignored by her mother and under surveillance by authorities because she can read, Amy reluctantly finds herself befriending Axel-a strange boy who claims to have come from a mythical place called ...Outside. Is Axel crazy? Amy knows there is no such place as Outside.
It is one I know that was published in 1980, but similar plots are used in a lot of works.