What's the must-see thing in Cusco?

Coricancha sits on Avenida El Sol, which runs southeast from Plaza de Armas. The surviving Inca walls inside are polished dark andesite, cut so precisely that you can run your fingertips along the seams and feel nothing but smooth stone. The Spanish demolished the gold-plated upper structure in the 1530s and built the Convent of Santo Domingo on the foundations. What survives is the Inca lower coursework. It is the finest masonry of its kind left in Peru. The curved retaining wall along the garden side catches morning light around 7:30am in August. The stone surface warms from near-black to deep grey-brown. Entry costs 15 soles, about $4.45 at current rates. The site opens at 8:30am Monday through Saturday, and you want to be among the first inside. By 10am the courtyard fills with guided groups and you lose the quiet that makes the stonework register.

Sacsayhuaman sits about 2 km uphill from the plaza, at roughly 3,700 metres. The largest stone weighs an estimated 125 tonnes, and the zigzag walls run about 400 metres across the hillside. Wind off the Andes cuts through fleece at the summit. August mornings currently hover around 5°C before the sun clears the ridgeline, so bring a down layer. The site is included in the Boleto Turístico, a 130-sole pass that covers 16 sites across Cusco and the Sacred Valley over 10 days. Worth noting, that pass is the only way in. You cannot buy a single-entry ticket to Sacsayhuaman. If your lungs are still adjusting to the city's elevation, skip the uphill walk on day 1. Take a taxi for 8 to 10 soles instead.

Cusco Cathedral faces the north side of Plaza de Armas. Construction began in 1559 and took nearly a century. Inside, the cedar choir stalls date to the 1600s, and the air smells of old wood and candle wax. The painting worth finding is Marcos Zapata's Last Supper. Zapata put a roasted cuy on the table in front of Christ. That single canvas says more about Cusco than a full-day guided tour. Entry is 25 soles, about $7.40. Mind you, altitude will likely hit before any sightseeing matters. At 3,400 metres, headaches and shortness of breath tend to set in within the first 6 hours. Drink coca tea, which is still offered free at most hotel front desks. Avoid alcohol on your first night. Plan day 1 around Coricancha and the Cathedral, both flat walks from any San Blas or central hotel.

The sequence matters more than the list. On day 1, walk from your hotel to Coricancha in the morning, then cross to the Cathedral after lunch. That is about 2 km total on flat ground, enough while your body acclimates. On day 2, take a taxi to Sacsayhuaman and add Tambomachay and Puka Pukara on the return drive. All three are covered by the same 10-day pass. Day 3 belongs to the Sacred Valley, where Pisac sits about 30 km north and Ollantaytambo roughly 75 km by road. Cusco punishes first-day ambition. The visitors who try to see five sites on day 1 are in their hotel room with a splitting headache by 3pm. Save Sacsayhuaman for day 2.