You step out into a thin, cold dawn in Cusco, the city’s terracotta roofs under a sky the color of old silver. Over the next week the Andes will test your breath and reward your patience: a rail ride through river-cut valleys to Machu Picchu, a high-alpine walk to the turquoise Humantay Lagoon at 4,200 m, and the striped slopes of Vinicunca—Rainbow Mountain—rising above puna grasslands. On the coast the desert pushes toward the sea; at Paracas salt-sprayed rocks host colonies of sea lions and Humboldt penguins while Huacachina’s dunes dare you to slide down them.