Hi I'm looking for an old scifi book that I read back in the 70s There is a space station in our solar system built by people who left to explore the universe long ago. The people living aboard it now are much less advanced. A stranger shows up who knows things about the station that no one else does. Turns out he is from the people who built it and they want it back to go explore other universes. I think it was old when I read it. Thank you for any help.
I remember that he could get to parts of the space station that the people living there could not. It was a paperback I think there was a picture of a space station on the cover. I'm pretty sure it was not an Ace double book. Not much to go on I'm afraid Stand alone book not series printed in US The people living on it know very little about the people who built it they have space travel but don't like to explore.