“The art of Joachim Patinir revels in a world that is earthly, visible, concrete,” observes the Spanish writer Antonio Muñoz Molina at the start of “Imagining the Real,” a lecture celebrating the two hundredth anniversary of the Museo del Prado in Madrid.

You must stand for a long time before his Rest on the Flight into Egypt to grasp each of the minute details the painter has gathered into the rather small rectangular space of the panel — if he has n...