Nam Tso is one of the most beautiful lakes in Tibet. It is located about 235km northwest of Lhasa in Damshung county. The lake sits at 4718m / 15,475 feet above sea level. A sign at the park entrance lists Nam Tso as the highest lake in the world, but I know of many lakes in the Changtang region of Tibet that are higher than Nam Tso. The lake is frozen for many months out of the year. When it thaws, it is a deep turquoise color. The snow-capped mountians in the background make it one of the most scenic places in Tibet.
The small monastery of Tashi Dor is located near the main tourist area of the lake. The monastery has just a handful of monks who live there. There are two large rock towers near the monastery that are always draped with prayer flags and khata (traditional Tibetan scarves). Entrance into the monastery is free.
Along the way from Damshung town to Nam Tso, you pass by many nomads living in black yak hair tents. This is one of the best places in the greater Lhasa region to see traditonal Tibetan life. You can see many herders with their yaks. It is possible to camp at Nam Tso. There are several tents where you can stay at as well as numerous little shops and restaurants to choose from. You can take a short horse ride near the lakeshore for Y10.
Getting to Nam Tso from Lhasa is easy. Many travel agencies arrange 1 and 2 day trips to the lake. Most of the one day trips to the lake cost Y200 per person. You leave around 7am and return to Lhasa around 7pm. For Y250 or so you can take a 2 day trip that includes staying the night at the lake. If you have a group of people I would recommend renting a private vehicle to go to the lake. Yes, it is going to be a little more expensive, but you can stop at several of the nomad camps along the way and spend time with the Tibetans who live there. The best time to go to the lake is in the early fall when there are not as many tourists. Winter is another good time to go to the lake, though the road to Nam Tso can often be closed due to snow. Going up to Nam Tso you have to cross over the 5190m / 17,023 feet Kong La Pass which can be impossible at times in the winter.