Historically, this was a caravan trail, one branch of the ancient Silk Road. More recently, the Chinese and Pakistani governments have built a highway.
It is the highest border crossing in the world, over 4800 meters (roughly 16,000 feet) in the Khunjerab Pass at the border. For comparison, Mont Blanc, the tallest mountain in Western Europe, is 4810 m and Mount Whitney, the highest point in the 48 contiguous United States, is 4421.
It may be the ultimate challenge for the devoted cyclist. There are organised bicycle tours, and several books about bicycling this route. Unfortunately the border is not open for cyclists. Everybody has to board the bus in either Tashkurgan (China) or Sost (Pakistan). From the Pakistani side you CAN cycle up to the pass, but not over it. You will have to return to Sost to take the bus.
Choose your time carefully. The highway is open around the year, though the tourist time is usually from May till late November and beware closures on religious or public holidays. It's a tough terrain and expect landslides during rainy season. Road condition is very good as the governments of Pakistan and China have reconstructed the highway. It is not advisable to take cars, 4x4 is preferred but a Van / coaster would serve the purpose. Besham is the start of Kohistan which is famous for its ruggedness and stubbornness. It is highly advisable to limit your stay and keep going preferably during day time. Kohistan borders Baltistan which is relatively safe. Main town to stay overnight is Chilas.
The KKH section from Besham to Gilgit is dry and warm. In summers, the temperature may go as high as 40 Celcius (Chillas is known as Sibi of Baltistan). Keep yourself well hydrated.
As of July 2013, there are two police checkpoints along the highway in China; for those leaving Kashgar, the smaller one is before Karakol Lake, and a larger one before Tashkurgan. These may slow down your journey significantly if there are many cars and trucks. As of July 2016, a pass is needed to do the crossing. For Chinese nationals, the crossing permit can be attained in Tashkurgan. Foreigners were rejected at the Tashkurgan branch, but may be able to get one in Kashgar.
The Pakistani section of the highway officially starts from Hasan Abdal, 60 kms from Islamabad. Chinese section starts from Kashgar, a major city in Xinjiang Autonomous Region , 1479 kms from Urumqi.
The highway passes the Hunza Valley The Hunza was the original Shangri La that inspired the novel (and later movie). Hunza is known for its orchards, welcoming hospitality and beautiful scenery.
From Kashgar in China, the list of towns and travel time from previous town are:
Hunza is one of the most peaceful region in Pakistan so the travellers do not need to worry about the security there, you are free to go anywhere, Just avoid drinking the tap water use mineral water, If you are in upper Hunza (Gojal) then you can drink the tap water, its clear and it comes directly from the spring.