Hanover is known as the 'green city'. Its overall urban area covers 200 km², around 10% of which consists of green areas. This has given Hanover its title of 'green city'. The best-known landscaped park in Hanover is the Herrenhäuser Gärten, the venue for both classical concerts and the International Fireworks Festival. For visitors interested in culture the city offers a wide range of museums. The most important and most visited are the Lower Saxony State Museum, the History Museum, the Sprengel Museum and the Wilhelm Busch Museum. The city's leisure facilities are rounded off by a large number of theatres and cinemas. The Maschsee, the lake known as 'Hanover's blue eye', is a little to the south of the city. In addition, Hanover is surrounded by the so-called 'green ring', which is ideal for jogging, cycling and in-line skating. Hanover is known worldwide in particular as a trade fair city. It is home to the world's largest trade fair site, where the world's biggest computer fair, CeBit, takes place annually. In the year 2000 Hanover was the venue for Expo, and today the site is frequently used for major events and concerts.