A classic science fiction novel (1977) by Fredrik Pohl, IMHO his best: An asteroid is found orbiting the sun perpendicular to the plane of the ecliptic; it was inhabited a long time ago by a mysterious race of aliens who get named the Heechee for lack of any better ideas. The Heechee lived in burrows and left behind hundreds of clever faster than light spaceships. The humans never quite learn how to operate these things properly, but if you sit down in one, twirl the knobs, and press the "go" button, you'll end up . . . somewhere. It may be somewhere interesting, or it may be the interior of a star or the event horizon of a black hole. The novel concerns the trials and tribulations of the volunteers who zoom off in these things to see what they can see. Some of them survive the experience. They're gamblers living in a state of absolute fear.

It's a great premise, but the volunteer thing is a bit contrived. They're just random volunteers: Any arbitrary loser who can afford a ticket to this asteroid is allowed to fly away in (and frequently destroy) a genuine alien artifact which predates the existence of the human race. How plausible is that? Not very, but if you can manage some industrial strength disbelief-suspension, the rest of the book is one hell of a ride.

Pohl followed up Gateway with a number of sequels, which conformed to Wharfinger's Law of Diminishing SF Sequels: