Hrm, Gateway you kinda need to read the first one at least. It lays out his universe of humans discovering an alien transport system with no instructions, and

Hrm, Gateway you kinda need to read the first one at least. It lays out his universe of humans discovering an alien transport system with no instructions, and IMHO the novelty of that is the best part. In later books, they stumble around a little before (no big spoiler) getting a bunch of answers about the builders and finding them.