Non-Stop is a 1958 science fiction novel by Brian Aldiss. It was Aldiss's first novel. Originally published by Faber & Faber, it has been reprinted by a numbers of publishers in the UK and U.S. since then.
The main character, Roy Complain, lives in a tribe where curiosity is discouraged. With a small group, he leaves his home and moves into uncharted territory. What they find changes their universe.
The place where Roy Complain lives is a group of tunnels surrounded by vegetation. A priest named Marapper asks him to join a group heading into the wilderness. Their target is a place called Forwards. They move through the wilderness and eventually encounter a group of civilized people in Forwards. It is revealed that they are on a multi-generational starship. Order has broken down, and most of the passengers have forgotten they are on a ship. The ship is being maintained by mysterious people called "giants". From the ship's log, they discover that the ship returned to Earth, and by this time, it should be in Earth orbit. With the help of the Forwards people, Complain's group tries to dismantle the ship and attack the giants. It is revealed that Complain's people have become adapted to the ship and have, in effect, evolved to become different from normal humans. The ship's "Emergency Stop" is activated and it breaks into pieces. The book ends with Complain believing that they will be taken to Earth.
Orphans of the Sky by Robert A. Heinlein
Metamorphosis Alpha a role playing game that has many similar elements.