First of all, a big thank you to @Scherbula, who knew that this tunnel existed, then a big thank you to @Sonni_SP, who knew where it was, and last but …
The iron barred door is not locked. However, there is a sign "No entry" attached. The water is a few meters in the tunnel, then you can dry further in with a flashlight.
Salka Cave is located between Pasecnice and Stara Hut, on the slope of Skalka Hill. Slate was mined here in the 17th century. Mining stopped in the 18th century. The …