Buyant-Ukhaa International Airport — Ulaanbaatar, Mongolia

For decades, ULN was Mongolia's principal window to the outside world, tucked into the Buyant-Ukhaa valley just south of central Ulaanbaatar and hemmed in tightly by the surrounding hills. That confined setting, combined with the capital's brutal winters and high elevation above 1,300 meters, made operations genuinely challenging, limiting the size of aircraft that could use the single runway and constraining how much the airport could ever grow. Built up through the Soviet period as Mongolia's main link to Moscow, it later became the country's primary international gateway as Mongolia opened economically after 1990, handling MIAT Mongolian Airlines alongside a growing roster of foreign carriers. As Ulaanbaatar's air traffic outgrew what the site could handle, international scheduled service eventually shifted to the newer Chinggis Khaan International Airport built farther from the city, leaving ULN's role considerably diminished, with its future use still evolving.