Peru is South America's most complete destination: Machu Picchu and the Inca heartland, one of the world's great food cities (Lima), the Amazon rainforest, Lake Titicaca, and desert coastlines — all in one country, at excellent value.
The classic first trip is 8–10 days: Lima (1–2 nights for the food), fly to Cusco, acclimatize in the lower Sacred Valley (2–3 nights), Machu Picchu (the big day), then Cusco itself (1–2 nights). Add Lake Titicaca or the Amazon with more time.
Altitude is the one real planning factor: Cusco sits at 11,150 feet. The smart itinerary lands in Cusco and immediately descends to the Sacred Valley (9,000 ft) for the first nights, saving Cusco for last. Coca tea, hydration, and an easy first day handle the rest.
Peru suits culture lovers, hikers (the Inca Trail books out months ahead), foodies (Lima alone justifies the trip), and adventurous families. Tourist infrastructure on the classic route is excellent.