Ghyakar village, Upper Mustang, Nepal

© Frank Bienewald/Alam

Trek on the roof of the world. High trekking season in Upper Mustang

If you’re lucky enough to be one of the thousand or so tourists allowed into Upper Mustang each year, spring and autumn are the best times for trekking through this incredibly dramatic landscape. Tucked into a remote region of Nepal, it’s geographically part of the Tibetan Plateau. The area is surrounded by the Annapurna and Dhaulagiri mountains and marked with deep gorges, terraced fields and colourfully stratified rock formations. But perhaps most fascinating of all are the sky caves, with 10,000 or so caves dug into the sides of valleys in several areas of the district. Some of these man-made caves are thought to be ancient burial chambers; others are richly decorated with valuable Buddhist paintings, sculptures and artifacts from the 8th to the 14th century. Perched 150 feet over the valleys, the questions of how they were built, what they were all for or even how people accessed them remain a mystery.