This is an established idea. I am unsure who first wrote it, but the idea runs as follows: a generation-colony ship has been in space for a very long time. Some disaster has overtaken it and now, long after the original crew are dead, the inhabitants have forgotten that they live on a travelling ship.
A deep space colony ship, hundreds or thousands of years out, has been overcome by disaster. The systems do not work as intended. The current passengers, descendants of the original crew, do not understand their environment and do not know that they are on a ship. Their world appears to be a post apocalyptic one, with mysterious machines and bizarre cul-de-sacs of societies. The adventurers explore this massive place, encountering weird creatures and peoples, slowly putting together the pieces to reveal the true nature of their world. The feel of the stories is one of mystery, with X-files and Lost overtones.
This specific idea became the premise for Metamorphosis Alpha.
Despite it’s now cliche’d idea, this has marvelous opportunity for a long running series. We do not need to reveal much each time. The protagonists explore and adventure in what appears a post-apocalytic environment, with elements appearing and disappearing without appraently making immediate sense – much like The X-files or Lost.