As I approach the bridge’s guardrail, there is a hush. I catch sight of a hel­meted man poised on a wooden plank that extends into noth­ing­ness. This man is about 30, with curly dark hair, mir­rored sun­glasses and a fierce smile, and he’s star­ing at a patch of air in the mid­dle dis­tance between his leather boots and the rough­ness of gran­ite walls extend­ing a thou­sand feet below. Without warn­ing he exe­cutes a quick hop: an under­stated motion, but enough to send his body into a tight, silent spin. Now he’s falling away from the stan­chions beneath my feet at a left angle, accel­er­at­ing so fast that within three sec­onds his body is halfway to ter­mi­nal veloc­ity, the point when the down­ward force of grav­ity on an object yields to the upward force of drag. Suddenly the toy man comes out of his spin. I can just make out a hand grasp­ing for the small pilot chute that will save him, that will send up the only thing now pre­vent­ing his gut from com­ing apart—in a few more seconds—like a piece of fruit against the rocks. The tourists around me groan, as if watch­ing a sprinter weave through traf­fic, as if watch­ing a kind of audac­ity that feels both gor­geous and impossible...