Bowl of Heaven by Gregory Benford
When the Sunseeker laves Earth, bound for the planet called Glory, its crew knows they will never see home again. None of them can ever have imagined, however, what they will find along the way. A gargantuan object, with its own star nettled inside. The bowl shaped structure is following the same path as the Sunseeker and it has a habitable are the size of millions of Earths, A landing party is sent to the surface, where they encounter some of the structures inhabitants - wildly differing species, and not all of them friendly.