I’m convinced I read a book called “The Inheritors” about two kids living in a post apocalyptic society. I don’t know the author and all searches on this title find other books that aren’t it…
It's actually very similar to “This Time of Darkness” by Suzanne Martel, but after reading that I’m sure it’s not the one.
The book I’m seeking ends when the girl travels through the tunnels and nearly dies, then opens the door and finds the air is actually breathable and it’s safe. It’s a full book and not a short story… If anyone has any idea I would appreciate to know the author.