Larry Niven & Gregory Benford 
Bowl of Heaven 

When the Sun Seeker leaves Earth, bound for the planet called 'Glory, ’ its crew knows they will never see the Earth again. None of them can ever have imagined, however, what they will find along the way. A gargantuan object, with its own star nestled inside. BOWL OF HEAVEN. The bowl-shaped structure is following the same path as the Sun Seeker, and it has a habitable area the size of millions of Earths. A landing party is sent to the surface, where they encounter some of the structure’s inhabitants—wildly differing species, and not all of them friendly.