Essen began in the mid-9th century as home to a women's abbey, then during the Renaissance became an important coal mining town and later a major steel production center. The famed metal-working Krupp family opened their first foundry here in 1810. One of Essen's most interesting places is the Zollverein Coal Mine Industrial Complex, once the largest colliery in the world. Now a UNESCO World Heritage Site, it attracts 800,000 visitors a year, often hosting art exhibitions and performances.