Northwest Bulgaria country's gate to West, and where the national capital, Sofia , is located Southwest Bulgaria mostly mountainous part dotted with wintersport resorts Northern Thrace plains dominated by Maritsa River and its tributaries, with many ancient Thracian sites and the second largest city of the county, Plovdiv , Haskovo Bulgarian Black Sea Coast relatively undiscovered resort towns, as well as large industrial port cities such as Burgas , Golden Sands and Varna Central Northern Bulgaria cities with turn-of-theth-century architecture such as Lovech and Rousse , lying along great rivers including Danube, and Ludogorie , literally "wild forests" towards the coast.