Yadong, on the southern edge of Tibet, is where China meets India. Getting there takes you right across the roof of the world, a day-long drive from Lhasa. As I leave Lhasa and head south, towards India, the long and winding road traverses pristine lakes, many of which are sacred for Tibetans, their banks dotted with dozens of worshippers lying prostrate, yaks in tow. Our journey ends in the Chumbi Valley town of Yadong, a small, muddy and underwhelming frontier outpost that, in a sense, presents a perfect snapshot of the India-China relationship.