On the Mariazell Railway in the Dirndl Valley near Frankenfels is one of the most beautiful natural experiences of the Mostviertel: the Nix Cave. It is a stalactite formation worth seeing made of snow-white mountain milk - popularly called "Nix". The cave is 1,410 m long and has a difference in altitude of 70 m. The Nix Cave was once formed by large mountain movements with stress releases, which resulted in collapses, folding and scaling. Guided tours are possible for groups at any time by appointment.