Which science fiction classic is best read before the age of 18?S

We try all sorts of things to introduce our children to the books we love. But maybe part of getting your kids into classic science fiction and fantasy is picking the right books. Which science fiction and fantasy books should people read before they turn 18, in order to appreciate them fully?

Please include a picture or book cover for your chosen book. And please mention the title, and why kids and young adults will get more out of it. Thanks!

Top image: Book cover art by Michael Whelan.