The structure that really dominates Pilsen is the Cathedral of St. Bartholomew. Its building started together with foundation of the city and it was completed at the beginning of the 16th century. The cathedral is a national monument as well as housing the argillite statue on the main altar - the famous Pilsen Madonna.
http://www.pilsen.eu/tourist/visit/the-best-from-pilsen/st-bartholomew-s-cathedral/st-bartholomews-cathedral.aspx