Heritage Universe

Somebody was here first. Scattered across thousands of light years are the artifacts of a vanished species called the Builders — a hollow world, a beanstalk anchored to nothing, objects that do things no physics on file will permit — and every one of them is older than any civilisation now able to look at it. Nobody knows what the Builders wanted. Whole careers go by cataloguing the things and getting no closer to an answer. Charles Sheffield's sequence — Summertide, Divergence, Transcendence, Convergence and Resurgence — sends a badly matched party at the problem: an obsessive artifact scholar, a woman running a planetary government, and a scattering of alien species with incompatible motives, all converging on a double planet where one artifact is about to do something for the first time in millennia. Sheffield was a physicist, and it shows in the best way. The puzzles are real puzzles, the scale is handled with a straight face, and the aliens think differently rather than merely looking different. It is one arc with one answer at the end of it. Start with Summertide and read the five in order — the questions the first book asks are not rhetorical, and the series fully intends to answer them.