Thousandstar de Piers Anthony?
On the world called Eccentric a new Ancient Site has been discovered, and unlike others which are "dead" this one appears to be active and functioning. To determine which Sphere has the right to explore it and investigate its secrets, a competition is being held. Each competing team consists of a carefully-matched host and transferee pair, chosen for their complementary skills and knowledge. The tasks test all of the competitors' abilities to their limit and range from word puzzles to navigating past a black hole. However, both Heem of Highfalls and his transferee Jessica of Capella have deep dark secrets that may cost them not just the competition but their lives.