Steel, machinery, electronic equipment, motor vehicles, coal, and beer are the city's principal products, though it is increasingly dependent on service activities. Dortmund also has a large wholesale fruit and vegetable market. Dortmund was largely destroyed in World War II, which led to planned reconstruction on modern lines. Four medieval churches—the Propsteikirche, the Reinoldikirche, the Marienkirche, and the Petrikirche—have been restored, and the city retains four moated castles and the ruins of Saxon and Carolingian fortresses. Notable examples of modern architecture are the synagogue (1956) and the Westfalenhalle (Westphalia Hall; 1952), one of Europe's largest halls, which is used for conventions, exhibitions, and sporting events. In the 1980s a casino and a new town hall were constructed. The city is home to the University of Dortmund (opened 1968), institutes for molecular physiology and spectroanalysis, Münster University's Social Research Institute, and schools for social studies, journalistic research, mountaineering, mining, teacher training, and adult education. Dortmund features several museums, including the Museum of Art and Culture, which houses the “Dortmund treasure,” a cache of more than 400 gold coins; the Ostwall Museum, which features 20th-century art, sculpture, and graphic art; and a natural history museum. Pop. (2003 est.) 589,661.