There are many karst springs along the whole length of Cerničko Polje. We shall try to enumerate and describe them here, as and when we have investigated each one.

3.1...."FAIRY CAVE" KARST RESURGENCE SPRING  -  VRELO "VILINA PEĆINA"  -  ВРЕЛО "ВИЛИНА ПEЋИНА" :
...........[Also previously known as VILIĆ PEĆINA, ca.1896.]
This intermittent B-type (allogenic) resurgence karst spring has a very large cave entrance. It is located on the northern border of the polje-floor, below and to the west of the village of Ključ, at the tectonic (overthrust) contact between Eocene Flysch and Limestone, at an elevation of 850m. asl. This spring is one of the two sources of the short karst river "Ključka Rijeka".

Both the views of the entrance were recorded from the vantage point of the top (dry) entrance of the Izvor "Vilina Pećina" directly opposite. The vrelo was devoid of flowing water on both occasions and was even drier inside than when visited a year previously. During August 2005., the interior had a lake. In 2006., there was no lake.

Image CP3.3. (left)
A view of the general arrangement inside the entrance chamber.
(Photo :  Gergely Balázs, 12 August 2006.)

This cave is formed on massive fractures which are also evidenced in a spectacular fashion outside and nearby to the east in the polje.
Cavern collapse (block breakdown) processes here are aided by the enormous quantity and power of the resurging water in the wet winter months.
This resurgence cave (= vrelo) is the downstream outlet-vent from the massive phreatic conduit aquifer fed by certain ponors in the higher elevation of Gatačko Polje. The difference in variation between Q_min and Q_max  of the intermittent flow from this typical resurgence cave is very large. Q_{min (apparent)}  = 0 m³ sec­¹., whilst Q_max  = 50 m³ sec­¹. has only been guaged as the combined flow from both vrelo + izvor output at the nearby weir adjacent to the ponor.

......Image CP3.4. (above)
......Climbing up the steep, karst-corroded inside rear wall of the entrance chamber.
......(Photo :  Gergely Balázs, 12 August 2006.)

For various reasons, we are limiting further web-published coverage of this cave system.
The entrance area provides several interesting features. The images below indicate some of these.
The image on the left illustrates a large kamenitza in the entrance chamber. It is about 0.9m diameter at the water level. The image on the right illustrates the size of the limestone boulders just outside the entrance. A member of our team is providing a convenient scale behind the tree.
 
 

The wide upper entrance leads into a sloping series of dry passages, long abandoned by the exsurging water, which now appears from a separate orifice developed on the same neo-vertical fracture, but about 20 metres lower down near the polje floor.
This cave issues what is effectively "karst groundwater" percolating down through the hinterland of the adjacent karst massif. This is a permanent flow with little variation between Q_min and Q_max throughout the year. Thus, it provides the basic flow of the Ključka Rijeka all year round. It is therefore of no co-incidence that the leat carrying water to the ponor-mills 300 metres downstream takes off from below this cave rather than from its more massive but intermittent neighbour.
We have yet to investigate this cave system more thoroughly, together with its hydrology.

This is another permanent flow karst spring with little variation between Q_min and Q_max throughout the year. It's supply is the karst "groundwater" in the enormous limestone massif behind the spring. This water is potable.

We currently have no further information about this karst spring.