Boringly obvious of course, one of the best #SciFi writers ever so I assume that you all have this series on your shelf.
For those who missed it however; in this universe humans and other races interact and nobody trusts anyone of course. A megastructure is discovered (a #DysonRing, take all the matter in a solar system and wrap it around the sun in a strip) and representatives of three races attempt to understand and interact with it.
Hell of a sandbox! I think you'll like it!
#LarryNiven