Underground Tunnels of Pilsen
Atlas Obscura: "The city of Pilsen in the Czech Republic is best known for being the birthplace of the now world famous "pilsner" variety of beer, but its industrial history is very nearly as important. As early as the 13th century the populace of Pilsen began creating cellars two and three stories deep beneath their homes, many of them connected by a series of tunnels. These were mostly used for food and supply storage initially, including a large amount of beer thanks to the Pilsen's long history of brewing. But as the system of tunnels grew, they began to be used for waste, disposal and also water storage and transport. By the end of the tunnels' construction, the city had over 12 miles of underground passage ways and one of the most advanced sewer systems in the Czech Republic at the time."