Yesterday I finished re-reading Eon by Greg Bear.

Eon is a classic hard science fiction novel, dealing with a mysterious hollowed out asteroid that arrives in Earth orbit. Inside lie many mysteries and inevitably in a novel from during the Cold War, the Americans and the Russians fight over it. The postulation of a Soviet Union that survived into the future makes things look silly in retrospect, but otherwise it's a fine novel. The characters aren't particularly well drawn and are nearly indistinguishable for the first half of the book, but the flood of interesting ideas makes up for it.