We begin the most challenging day of our trek, winding our way past a gigantic terminal moraine left by a receding glacier as we begin the zig-zag ascent to the mighty pass of Incachiriasca (4900m). Around mid-day we cross the pass, a bare, windswept landscape of rocks and ice, close to cracking glaciers and the ridge spot known to climbers as Japanese camp. From here we descend into the valley of Sisaypampa, catching glimpses of Palcay (5,422m/17,785ft), the “hidden peak” just north of Salcantay. We camp at Sisaypampa.

We proceed northwards a short way downvalley, reaching the village of Huayllabamba, where we turn west up the side valley of Llullucha. Now we climb through shifting native microclimates of tropical cloud forest then high altitude queñua or polylepis forest, all draped with bromeliads and orchids, before crossing a brief belt of native dwarf forest, filled with hummingbirds. We break through the treeline, crossing the rim of Llulluchapampa, a 3,800m/12,460ft plateau.

We pick up the trail which traverses a steep, grassy mountainside to the second high pass of our journey – and first pass of the famous Inca Trail to Machu Picchu – Warmiwañusca (Dead Woman’s Pass) – at 4,200m/13,775ft. Here we can look back on a vast panorama of sweeping snowpeaks and valleys of the Huayanay massif, or gaze ahead to the deep Pacamayo valley and the climb to our third high pass, the Abra de Runkuracay (4,000m/13,120ft), which awaits us tomorrow. One and a half hours of descent from the pass on a paved trail, with a waterfall to our left, brings us to our campsite in the forested Pacaymayo valley (3,600m/11,800ft).

As we climb out of the Pacamayo valley up an orchid-strewn mountain slope past the Inca site of Runkuracay, we follow an Inca stone stairway and encounter awe-inspiring views across the Urubamba gorge to the glaciers of Wakay Willka (5,750m/18,860ft).

As we reach the next pass we confront a sweeping panorama of the snow-covered Vilcabamba range ahead of us, dominated by Choquetacarpo and Pumasillo (5990m/19,650ft). We descend, making a stop to visit Sayacmarca, the first of several intricate and beautiful Inca ceremonial sites along the trail. Continuing along a winding stone highway along the upper fringes of the Andean cloud forest, we pass other small Inca sites and platforms, and enter a tunnel cut from living rock, before reaching our camp above another Inca ruin, the site of Phuypatamarca.