At the Hussite Museum in the former Town Hall, you'll find the entrance to a fascinating 650m stretch of underground passageways, which you can visit by guided tour only. The passages, constructed in the 15th century as refuges during fires and times of war, were also used to store food and to mature beer. Temperatures underground can be chilly, even in summer, and the paving stones are slippery, so be sure to dress accordingly.