Uzbekistan is a landlocked country in Central Asia, and it is one of only two 'doubly landlocked' countries in the world (meaning it is surrounded entirely by other landlocked countries). The capital is Tashkent. Its geography is dominated by vast deserts, including the Kyzylkum, and fertile valleys like the Fergana Valley. Historically, Uzbekistan was the center of the ancient Silk Road, with the cities of Samarkand, Bukhara, and Khiva serving as major hubs for trade and culture. The country is a major producer of cotton and gold. One of its biggest environmental challenges is the drying up of the Aral Sea, once the world's fourth-largest lake, which has shrunk to a fraction of its former size due to Soviet-era irrigation projects.