For a scenic browse, and an answer-page for Guess The World...
He now saw that some of the larger rocks were strangely angular. Pushing some around, he noticed more. Calling Arpad, they explored the area thoroughly. There were many such angular rocks, and now in several spots they noticed that one or two such were still perched on top of others. Bruce found a little piece of reddish stuff, plastic of some sort, probably part of a machine, though he couldn't place it. Arpad turned up some bits of broken material which looked like splinters of a smashed vase or pot.
When they came back to Garcia, and sat around and discussed their findings, they knew they had come across one of the most amazing discovering in interplanetary history. Clearly there had once been a city standing in this plain on Mimas. A city that had crumbled into ruin and dust probably hundreds of thousands of years ago - and a city that defied all the logic of life.
explained this, "How could life survive here? There could never have
been enough air here, even when this satellite was new and still hot
from its creation. My guess is that this city was a colony planted from
somewhere else. But where and who could it have been that was here so
many lost ages ago - back before there were even men on Earth...?"
Donald A Wollheim, The Secret of Saturn's Rings (1954)