Bojanova cave
For a long time the Predjama Cave System has been the second largest cave system in Slovenia and the struggle for the second place isn't been decided yet. The system was carved by disappearing spring Lokev which runs all the way to Vipava. The connection with Vipava valley was allegedly confirmed in the 19th century for the first time using wood sawdust. After the Second World War it was confirmed using more modern methods.
Huge potential of Predjama system has so far attracted many generations of Slovenian cavers that have been exploring the system for over hundred years. We are proud to have played an important part in it's exploration. The system behind Predjama castle spanned over 13km of underground shafts. With new discoveries in 2009 it has grown to over 14km as in March 2009 members of DZRJ Luka Čeč have after several years of exploration finally connected Bojanova cave with Predjama Cave System.
Lenčkova cave
Entrance in Bojanova cave is located 740m north of Predjama castle. We discovered Lenčkova Cave in 2005 when searching for possible alternate entrance to Predjama Cave System. Despite our high hopes we soon reached the end of cave and failed to find connection with Predjama Cave System . Exploration of Lenčkova Cave has ended to soon and we decided to look for connection on the other side in the West branch of Predjama Cave System. that lies 150m beneath Lenčkova Cave. We decided to climb chimneys in our effort to ascend to Lenčkova Cave. Unfortunately all chimneys ended with impassable squeezes without any air current. In March 2006 we started climbing a vast chimney in a recently discovered parts of West branch following a hint from our senior member Jurij Hajna. Despite it's size there was a noticeable air current in the chimney which was very promising. After two months of weekend actions we climbed 110m of it. Judging by the position of new parts we estimated that we were approximately 30m bellow the surface and 150m east of Lenčkova Cave. At that point we realized that we are far from connecting it with Predjama Cave System. However this course of development led us to another discovery. In woods above Predjama Cave System Janko Marinšek showed us a promising breathing hole that they were digging more than a dozen years ago.
Bojanova cave
Summer of 2006 has passed by with intensive digging in the Bojanova cave which was just a 4m deep breathing hole at that time. Soon enough we reached a 30m deep abyss with a somewhat big hall in the upper half that is spreading in more horizontal tunnels. Quite some time has passed in search of continuation but eventually we found an air current behind the mud fall at the end of the hall and started digging. 
It took us entire 2007 to dig our way through a muddy rock fall that proved to be a joint along which a cave has formed. After further digging we passed horizontal passages and through huge rock (Kamnoljom) blocks arrived to a steep descent into the depths. By the end of the year we did some more digging and explored several parallel shafts only to reach a rock filled bottom of Bidala abyss. We estimated that we missed the connection with Predjama cave system given the fact that we descended over 100m below the estimated connection. The Bidala abyss was a dead end so we searched for continuation at higher levels. In the beginning of 2008 we found a current of fresh air at depth of 45m. For next two months we were following the air current and dug along the known joint. By the end of February, when digging became increasingly dangerous due to potential collapse, we decided to measure the cave polygon. Luckily it turned out that we stopped digging only a few meters away from the explored parts in Predjama Cave System. We decided to organize another action to confirm or overthrow connection between Bojanova Cave and Predjama Cave System. The plan was to send two groups; one with smoke-rockets in Predjama Cave System and the other to see if smoke gets through to Bojanova Cave and how long it needs. We planned to use radio Nicola for communication.
O happy day
And so came the day (Sathurday 21.3.2009) when enough of us had time to execute a two group action. But just before we gathered Ivo miss-connected the battery on radio Nicola and fused it. We decided to go on with the action but the absence of radio was a big problem. How are we supposed to communicate if knocking with hammer was inaudible? How will we know when both groups are in their places? How long should we wait for smoke to appear? There was a big black cloud looming over our mission. Anything but optimistic we went each to it's cave. My group went in the Bojanova cave. It took us about an hour to reach the rockfall. As we waited there we were quiet for a while and I thought I heard the other team. We stayed quiet for a little longer but nobody heard a thing. I crawled a little further alongside the rockfall and listened. 
This time I clearly heard voices although still faint. My team mates still heard nothing and joked that I must have been smoking something funny. But then someone from the other team yelled. We all heard that and started yelling back from the top of our longs but no one answered. I guess they didn't hear us. All of a sudden we heard a voice loud and clear saying: “Hey, where are you?” “Here!” I replied and shined a light between the rocks. Marjan on the other side has done the same and at that point we realized how close we really were. We could literally shake our hands through the rockfall. Our joy was immense. Such a discovery happens once in a lifetime if you're lucky. The good news was also the fact that the rockfall could be easily removed from the other side.
Bonus akcija
Soon after the discovery we took our tools and headed in the Predjama Cave System to remove the last remaining rocks to Bojanova Cave. But before we got to the chimney we ran in to a almost completely water filled passage while a passage further in cave was completely flooded. It took us by surprise because both passages were dry every time we were in the cave. We could have waited for water to dry out but we were too excited. From various pieces we made a 45m long hose and used it for natural suction and left it running over night. When the water was out of our way we finally went up the chimney and removed the few remaining stones between Predjama Cave System and Bojanova Cave.
Radio positioning
When researching and surveying the cave system we used radio Nicola for communication and projecting points in cave on the surface. The later needs two units each equipped with a coil (Ø50cm). The transmitting unit is in cave with coil placed horizontally creating a vertical beam of magnetic force. The receiving unit the surface is spinning in vertical position and must be moved arround moved around. When placed in center of magnetic beam the receiver makes no sound no matter how the coil is oriented along the vertical axis. This also means that the receiving coil is exactly above the transmitting coil.
Short timeline
| 04.02.2006 | First visit of the chimney in the new parts of the West Branch |
| 14.05.2006 | Reached the top most part (110m climbed) |
| 05.08.2006 | Breached the entrance to the Bojanova Cave |
| 06.01.2007 | Found an air current behind muddy rockfall |
| 23.03.2008 | Descent to the bottom of the abyss Bidala (-142m) |
| 28.12.2008 | At a depth of-45m discovered air current |
| 21.03.2009 | Confirmed connection |
| 01.05.2009 | Caves connected |
| 23.05.2009 | The first trip through Bojanova Cave to Predjama |
Workers and associates:
Boris Šajtegelj, Ivo Sedmak, Jernej Petrovčič, Jože Pristavec, Marko Matičič, Matjaž Milharčič, Simon Klemen, Tomaž Česnik, Dušan Tominc, Izidor Šantek Zupančič, Marjan Vilhar, Matija Perne, Roman Bogataj, Stanislav Glažar - Sten, Zdenka Žitko
Blog of activities that led to connecting caves
| 9. 8.2005 | Ogled kaminov v Predjamskem sistemu |
| 4. 2.2006 | Plezanje kamina |
| 1. 4.2006 | Plezanje kamina v Predjamskem sistemu |
| 18. 8.2006 | Kopanje in meritve v Bojanovi jami |
| 8.10.2006 | Radio lociranje |
| 7. 1.2007 | Bojanova jama |
| 10. 6.2007 | Vrtanje v Bojanovi jami |
| 22. 3.2008 | Rušenje podora |
| 1. 3.2009 | Meritve v Bojanovi jami |
| 1. 5.2009 | Preboj Bojanova jama - Predjamski sistem |
| 23.5.2009 | Skozi Bojanovo jamo v Predjamo |