It takes eight days to reach the base camp of Nanda Devi on the south side. The Rishi Ganga River forces its way through two gorges. The first one, near Lata village, cuts off any possibility of an easy approach, and therefore a route over two intervening ridges -the Dharanshi and Malathuni – was explored. Shipton and Tilman called this the Curtain Ridge. Near the second gorge of the Rishi Ganga a route was explored over precarious, rocky terrain.
The approach to the inner sanctuary will always be difficult. The route is: Lata, Lata Kharak, across Dharanshi Pass (4267m/14000ft) to Dharanshi Alp, across Malathuni
Pass (4270m/14010ft) to Dibrugheta Alp, along the river to Deodi, Ramni at the foot of the gorge, Bhujgara half way through the gorge and Patalkhan across the main difficulties of the gorge. 'The Slabs' are the first of the challenges, where downward-sloping rocky slabs make for a precarious crossing. A narrow staircase of stones ahead cuts across a huge wall. Just one slip and you would plummet thousands of feet down the gorge, aptly called the vaikunth seedi (the 'staircase to heaven') by locals. If you climb up this, you will reach the heaven of the Nanda Devi Sanctuary, whereas if you fall, you might reach heaven anyway. Patalkhan is the first halt in the sanctuary. From Patalkhan, the route crosses the Rishi Ganga to enter the north side of the sanctuary.
The optimal timing for our trekking trips is between May 1st and June 30th and between September 1st and October 15th. Both seasons have their attractions. During the month of May the spring flowers bloom at the margins of the snowline while the weather is generally settled barring the occasional pre monsoon storm that can blow up at any time. Day time temperatures can rise to the mid 20s even at altitudes while at night they can fall to 0 degrees C. The post monsoon season is a time of settled weather with clear views of the mountains.
Day time temperatures will still be quite warm, upto 20 degrees C during the middle of the day, however at night the temperatures will occasionally drop below 0 degrees C.