Looking south from the roughly 20,000 foot Pik Dankova in Kyrgyzstan (near the China border), it is possible to see deep into China’s Kunlun Mountains with many peaks over 300 miles (483 km) away. This is made possible by a broad low-lying desert plain separating two very high mountain ranges at just the right distance.
As pointed out by jbramel, what is even more astonishing is that there is a 21,000-foot peak visible at an incredible 334 miles (538 km)! This is visible (also according to this panorama tool) looking in a direction 169.7 degrees S from Pik Dankova and just might be the longest line of sight possible on the surface of the earth.
Link to computer-generated vista: http://bit.ly/1f8SQRB
So… any intrepid climbers want to lug a camera and telescope up there?