About 20 km south of Rangdum stands the Penzi-la watershed across which lies Zanskar, the most isolated of all the trans-Himalayan valleys.

The Penzi-la Top (4401 mt) is the picturesque tableland adorned with two small alpine lakes and surrounded by snow covered peaks. As the Zanskar road winds down the steep slopes of the watershed to the head of the Stod valley, one of Zanskar's main tributary valleys, the majestic 'Drang-Drung' glacier looms into full view. A long and winding river of ice and snow, the 'Drang-Drung' is perhaps the largest glacier in Ladakh, outside the Siachen formation. It froms the cliff-like snout of this extensive glacier that the Stod or Doda River, the main tributary of river Zanskar, rises.

The fertile region of Padum and it's outlying villages and gompas form the nucleus of Zanskar. Zanskar comprises a tri-armed valley system lying between the great Himalayan range and the Zanskar mountain.  It is mainly along the course of this valley system that the region's 10000 strong, mainly Buddhists, population lives. Spread over an estimated geographical area of 5000 sq.km, high rise, mountains and deep gorges surround Zanskar. The three arms radiate star-like towards the west, north and south from a wide central expanse where the region's two principal drainages meet to form the main Zanskar river.

The area remains inaccessible for nearly 8 months a year due to heavy snowfall resulting in closure of all the access passes, including the Penzi-la. Today, Zanskar has the distinction of being the least interfered place as compared to Ladakh, and one of the last few surviving cultural satellites of Tibet. There are a lot of ancient yet active monastic establishments. The area's uninterrupted Buddhist heritage has been principally due to it's isolation.