The wreck sleeps in darkness, a puzzlement of corroded steel strewn across a thousand acres of the North Atlantic seabed. Fungi feed on it. Weird colorless life-forms, unfazed by the crushing pressure, prowl its jagged ramparts. From time to time, beginning with the discovery of the wreck in 1985 by Explorer-in-Residence Robert Ballard and Jean-Louis Michel, a robot or a manned submersible has swept over Titanic’s gloomy facets, pinged a sonar beam in its direction, taken some images—and left.