The border between Afghanistan and China as at the end of the Wakhan Corridor, an odd looking thin tendril of land separating Tajikistan from Pakistan. The border itself is only 57 miles long.
It was established in an agreement between the British and the Russians in 1895, although the Chinese and Afghans did not finally agree on it until 1963. The Chinese side is in Xinjiang where all the Uyghurs are banged up.
This arrangement is so ludicrous that it would be funny if it wasn't so mad and bound to end in tears.