"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"—magnificent views that inspired and terrified at the same time.

Some things never change. Three