The Sword and Laser discussion

So they just had their first encounter with the natives and ran away after failing the god-test. The natives are clearly some offshoot of humanity from earth.

So now I'm wondering if a much more advanced race built the ring and then kidnapped some humans and put them there for whatever purpose (an experiment? Observation?).

Did future humans come back in time and build it for some strange reason?

The people who built it seem to have abandoned it, will they show up?

Don't tell me the answers, I'm just wondering, and hoping it will be an interesting thoughtful reason, not one of those endings where we don't ever find out.

Also I'm hoping they will find a half-buried Statue of Liberty and Charlton Heston will show up screaming about damned dirty apes, because the earthlike ordinary-ness is getting boring.

There are some answers in Ringworld, but for more info you need to read two other Known Space books in particular:

(view spoiler)[The Ringworld Engineers and Protector (hide spoiler)]

the protector is one of my favorite niven books.