Between 25 and 35 million Kurds inhabit a mountainous region straddling the borders of Turkey, Iraq, Syria, Iran and Armenia. They make up the fourth-largest ethnic group in the Middle East, but they were denied a permanent nation state thanks to the Treaty of Lausanne.

Perhaps the world's most complicated boundary, a narrow bike trail offers a window into a region that has been the battleground of Europe and is where culture and geography intersect.