The German boarding school in Plön Castle was closed in 2001 under the state government of Heide Simonis and the castle was sold to the Fielmann optical company. They re-opened it in October 2006, after extensive restoration work, as a school for opticians. The total cost of refurbishment and reconstruction was 35 million euros. Today it is a non-profit training centre for the whole field of optics. This has strengthened the economy of the town of Plön, which has become more widely known, even internationally. Each year the castle is home to six thousand Fielmann employees who receive training for anything up to a two-week period. Other students at the castle take part in B.A. and master optician courses. The castle has extensive grounds and is one of the most beautiful castles in Schleswig-Holstein. There are several restored historic buildings - such as the Princes' House ("Prinzenhaus"), Old Swimming Baths ("Alte Schwimmhalle"), Clock House ("Uhrenhaus") - as well as shady avenues and old trees open to the public to stroll through and explore. Parts of Günther Fielmann's own antique collection can be viewed at the castle; it encompasses pieces from the major north European and French epochs since the mid-seventeenth century.