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Is Step into the Void, a new 12,650-foot (3,856-meter) perch in the French Alps, the scariest? A person stands in the 'Step into the Void' installation in the French Alps. PHOTOGRAPH BY ROBERT PRATTA, REUTERS/CORBIS Roff Smith for  National Geographic PUBLISHED JANUARY 22, 2014 "I must have torrents, rocks, pines, dead forests, mountains, rugged paths to go up and down, precipices beside me to frighten me," wrote  Jean-Jacques Rousseau  of his love of rambling in the French Alps. "The odd thing about my liking for precipitous places is that they make me giddy, and I enjoy this giddiness greatly, provided I am safely placed." Rousseau wasn't alone in his fondness for precipitous places and giddy feelings. All around Europe, 18th-century ladies and gentlemen on the "Grand Tour"  were scrambling up mountains, peering into abysses, and standing on the edges of cliffs in a quest for what they called "the sublime...