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Großer Garten (Great Garden) in Dresden, about 1.8 square kilometers. At the center is chateau that served as a getaway for the Saxon royal house. It also contains lawns, fountains, ponds, a botanical garden, a zoo, an amphitheater and a few other installations. Across one of the main entrances is the city's football stadium.
Admittedly there's a VW factory in one of the corners nowadays, but that section had always been built up with exhibition halls and was never botanical, and that factory is designed to be toured by visitors and dedicated to building high end models like the VW Phaeton and certain Bentley models and now the electric VW ID3. It also runs freight trams across the city for supplies.