Baku is the capital, largest city, and largest port of Azerbaijan and the Caucasus region. The city consists of two principal parts: the downtown and the old Inner City (21.5 ha). Baku's urban population at the beginning of 2009 was estimated at just over two million people.
The Inner City of Baku along with the Shirvanshah's Palace and Maiden Tower were inscribed as a UNESCO World Heritage Site in 2000. According to the Lonely Planet's ranking Baku is also amongst the world's top ten destinations for urban nightlife. (source)
Thank you Tural!