The structure is, in fact, an underground drive of a former iron-mill. Because of the length of 150 m and the tunnel height 6 m, the work is truly unique. In this passage, the whole Ploučnice River was directed, running through some 50 m between tall sandstone walls to disappear in the right angle in a tunnel. After a short time, the water appears in an open recess, to proceed through the long tunnel. In the 19th century, a local miller used to take visitors for a ride at night by torch light, and the visitors were really amazed with the technical miracle.

Locality: Near the village Noviny pod Ralskem, 3 km to the southwest of Stráž pod Ralskem.