Dubnica opals originate in the world-known deposit in Slanské vrchy near Prešov from the locality between villages Zlatá Baňa and Červenica. Dubnica Opal Mines lived their golden age between 1845 and 1880 when Viennese jeweler Solomon Goldschmidt was their tenant. Goldshmidts were the ones who managed to present their opals to the world jewelry markets. The largest piece of valuable opal in the world comes from Dubník - it was found in the riverbed of Oľšavka in 1775. It has a respectable length of 13 cm and weights 594 g (2870 carats). For its interplay with colors it was named Harlequin and is now stored at the Museum of Natural History in Vienna. Opal mines were closed in 1922. There are 22 km long underground tunnels and 1,5 km long section of William tunnel available to public. Dubnica opal mines were declared to be a protected site of hibernating bats. In winter there are 4 000 bats of 16 kinds.