This extraordinary 60-minute guided tour explores the passageways below the old city. The earliest were probably dug in the 14th century, perhaps for beer production or defence; the latest date from the 19th century. Of an estimated 11km that have been excavated, some 500m of the tunnels are open to the public. Bring extra clothing – it's a chilly 6°C underground. Tours are given in English at 2.20pm daily from April to October; check tour times and book tickets online.

　　Plzeň's wealthier set used to have wells in their cellars. Overuse led to severe water shortages. When wells dried up they were often filled with rubbish and buried; these have yielded an amazing trove of artefacts.