Non-Stop - Brian Aldiss

Curiosity was discouraged in the Greene tribe. Its members lived out their lives in cramped Quarters, hacking away at the encroaching ponics. As to where they were - that was forgotten.

When Roy Complain loses his wife, he decides to find out. With the renegade priest Marapper, he moves into unmapped territory, where they make a series of discoveries which turn their universe upside-down. Is their world really a world at all, or just a container moving between worlds...?