We think we know the world of Maurits Cornelis Escher with its mind-bending staircases and buildings that impossibly twist upon themselves. Yet a shocking glimpse of reality intrudes in Somerset House’s gripping journey through his metaverse. In 1945, Escher designed a diploma for students at a temporary academy in Eindhoven, recently liberated from Nazi rule. Behind a wise old owl in the foreground, twisting columns of black smoke rise from a riverside town, their evil sinuousness reflected in the water. The message of this depiction of war is not only that Escher was a civilised individual surviving a brutal age but also that his visual delights were never just fanciful. Even his wildest speculations reveal the workings of the world itself, grounded as they are in what Galileo called “the language of mathematics” in which “the book of nature is written”.