Riccardo Giacconi has probably seen deeper into the universe than any other human being. He has conducted his explorations not with the naked eye, but with a series of increasingly sensitive detectors, relentlessly searching for the source of cosmic x-ray radiation. In this first-person account of pursuing one question for 40 years, what emerges most clearly is the kind of focus, determination, and invention required to make discoveries in the Nobel Prize league. Giacconi confesses that “X-ray astronomy is not easy” – an admirable understatement – but he succeeds in proving three key points: from the Uhuru satellite to the Hubble and Chandra telescopes, the success of experiments depends as much on brilliant instrument design as on data analysis; individual, identifiable galaxies are the source of the universe’s x-ray radiation background; and so we are now “looking at objects whose nature we do not know” – objects that the next generation of astronomers will understand only if they have the resources to build new instruments.