American painter William Rimmer produced this enigmatic image in 1872. A man runs through a palace. Is he fleeing or pursuing? What is the ghostly figure in the parallel corridor beyond him? And whose shadow is entering from the right?

No one knows. “As the title confirms, the painting turns a general situation into an ambivalent one,” writes Victor I. Stoichita in A Short History of the Shadow (1997). “There have been numerous attempts to specify its contents, but these have only resulted in the principle being misunderstood, for everything leads us to believe that it was Rimmer’s intention to create a story that functioned through its enigmatic form.”