Sliven (Bulgarian: Сливен) is the eighth-largest city in Bulgaria and the administrative and industrial centre of Sliven Province and municipality.Sliven is famous for its Bulgarian Haiduts who fought against the Ottoman Turks in the 19th century and is known as the "City of the 100 Voyvodi", a Voyvoda being a leader of Haiduts.The famous rocky massif Sinite Kamani (Сините камъни, "The Blue Rocks") and the associated national park, the fresh air and the mineral springs offer diverse opportunities for leisure and tourism.