Off the western coast of Norway are sea caves graced by stick figures painted more than 2,000 years ago. Colored red from the iron-oxide pigment used by Bronze Age artists, the figures appear to be in motion, with arms and legs splayed. Among his travels in Underland: A Deep Time Journey, British nature writer Robert Macfarlane journeys to the remote cave called Kollhellaren on the tip of the island Moskenes to see its dancing figures. To arrive there, Macfarlane crosses a ridge of peaks called the Lofoten Wall, pulls himself out of a snow crevasse into which he had partway plunged, crosses...