A fascinating concept, one where humanity discovers an asteroid, hollowed out and developed into a space station by a seemingly extinct species. A space station that has thousands of spaceships that carry either 1, 3, or 5 persons and go to destinations that are unknown.
The protagonist, Robinette, develops throughout the story in an interesting way, and this mainly occurs through the use of an artificially intelligent psychiatrist, Sigfrid, who is counselling Robinette after Robinette has become wealthy and returned to earth.
The reasons behind all this, and the facts behind Gateway, are gradually revealed until at the end it all comes together and the story, to me, suddenly becomes so much better than it had looked like being up to that point.
A classic in the science fiction genre, clearly Frederik Pohl's masterpiece. Strongly recommended.