The walls of Inca Cusco survive beneath and beside what the Spanish built over them. The Qorikancha - the Temple of the Sun, most sacred site of the Inca Empire, its walls once covered in gold sheets that the Spanish melted - now supports the Santo Domingo church and monastery. The stones that fit together without mortar, cut so precisely that knife blades cannot slip between them, demonstrate engineering that the conquistadors could not match even as they destroyed what it created.

The Inca walls are visible throughout the historic center - the twelve-angled stone that fits perfectly into its neighbors, the retaining walls that hold terraces, the foundations that colonial buildings rest upon. The technique has not been replicated; how the Inca achieved their precision remains debated. The walls that survive are both engineering marvel and colonial metaphor, the indigenous foundation holding up what conquest imposed.

The Plaza de Armas was the heart of Inca Cusco, the gathering place where ceremonies and celebrations occurred, larger then than now. The Spanish rebuilt it to colonial proportions, surrounding it with the Cathedral and the Church of La Compania, the arcades that still line its edges. The plaza remains Cusco's center, the place where tourists gather and political demonstrations occur, the reference point from which distances are measured.

The Cathedral holds colonial art that includes the famous painting of the Last Supper with guinea pig as the main course - the Andean animal substituted for lamb by indigenous artists, the cultural syncretism that conquest produced visible in religious art. The churches that dominate the plaza were built from stones taken from Inca structures, the recycling of materials that the Spanish practiced throughout their empire.

Cusco's altitude - 3,400 meters above sea level - affects every visitor who arrives from lower elevations. The soroche, altitude sickness, brings headaches and breathlessness and nausea to those who have not acclimatized; the coca tea that hotels offer provides traditional relief. The thin air that the Inca accepted as normal requires adaptation that modern tourists must plan for.

The altitude shapes the city beyond its impact on visitors. The short breath that steep streets demand, the cold nights that elevation brings even at tropical latitude, the sunlight that burns more intensely through thinner atmosphere - these require adjustment. The Inca chose this site despite its altitude because the Sacred Valley below provided agriculture while the height provided defense. The location made sense strategically; comfortable it was not.

Cusco is where Machu Picchu begins - the city from which trains depart for Aguas Calientes, from which tours operate to the Sacred Valley, from which the Inca Trail starts for those who hike. The tourism infrastructure that has developed exists to serve visitors passing through to somewhere else; the hotels and restaurants and agencies fill the historic center with services that history alone would not justify.

The gateway function shapes Cusco's economy and character. The backpackers seeking budget transit, the luxury travelers seeking packaged experiences, the tour groups filling the narrow streets - these define the city's contemporary life. The Cusco that exists for tourists overlays the Cusco where Peruvians live, the historic center functioning as tourism district while residential life happens in neighborhoods tourists rarely see.

Sacsayhuaman rises above Cusco, the fortress whose zigzag walls of massive stones have survived five centuries. The stones are enormous - the largest weighing over 100 tons - fitted together with the precision that Inca engineering achieved everywhere but at unprecedented scale. The fortress was largely dismantled by the Spanish, its stones carried down to build colonial Cusco; what remains is impressive enough that the destruction's scope becomes comprehensible.

The site hosts the Inti Raymi festival each June, the celebration of the winter solstice that the Inca Empire made central to its calendar. The modern festival is reconstruction and tourism product, the ceremonies performed for audiences rather than gods. Yet the location matters - Sacsayhuaman overlooking Cusco as it did when emperors ruled, the connection to Inca cosmology maintained even as context has changed.