Frýdštejn, 468 32

Pseudo-karst cave is located in the valley of the Vazovecký brook about 3 km north of Turnov. It is part of the karst system and its known length is 225 m.

The cave originated on fissures, which were spread by dissolving sandy limestone. An underground flow with an average yield of almost 30 l /s rises from it, which is fed, among other things, from two known sinks, from Podhorčí and Roudný.
Ondříkovice sinking belongs to the natural monument, but water does not flow to Bartošova kiln. The natural monument bears the confusing name "Ondříkovice pseudo-karst system", which no longer corresponds to the current knowledge of the cave. We are talking about pseudo-karst only for insoluble rocks, such as quartz sandstones, which form rock towns of the Bohemian Paradise. The flow under the spring was used to drive a water wheel.
In the past there used to be a mill and later a glass cutter, which is now a recreational facility.
The name furnace is sometimes used in the Bohemian Paradise as a synonym for the word cave (Russian or Bulgarian pawn). Some of them resemble a bread oven.