Text: René Lipmann Photos: Jeroen Bijmans

From a subtropical swimming paradise in Weert to diving in a thermal cave system under Budapest. Diving instructor Jeroen Bijmans has come a long way. On Duikvaker he likes to talk about his greatest passion: cave diving.

Jeroen, where are your diving roots?

I actually came into contact with diving purely by chance. Instead of going to grandma and grandpa every Saturday, as a little boy I had asked to be dropped off at the new subtropical swimming paradise in Weert. Yes, there was a plastic palm tree and there were waves every fifteen minutes. Now almost 40 years later that palm tree is still there! In the same swimming pool there are also training pools where the local diving club practices. I saw that club there with extremely interesting equipment. When we moved to Weert and I was allowed to choose a club, it was quickly clear to me. Diving! I then took over the double 7 from my first instructor quite quickly. One with a pull reserve, because a manometer was so expensive. Just like a second regulator. So I practiced holding my breath and buddy breathing well. To this day I still benefit from that. We did our first open water dives at a campsite in Terspegelt in Brabant. It took a few more dives before I saw my first fish! Training was still done the old-fashioned way. Not only were the tables from the army. Later that became the beach park Aquabest. That was already much better since the McDonalds was around the corner. Nowadays my NOB association practices in the Boschmolenplas. Yes, I am still a member and have now climbed to NOB 2-star instructor. In addition, I am a member of the cave diving working group of the NOB

I remember as if it were yesterday your enthusiasm and passion during an introductory dive that you provided for 2 nephews aged 8 and 10. What makes teaching so special for you?

Diving is truly my passion. I have only been working professionally in diving for 12.5 years. Before that, my work was almost secondary. Fortunately, I had a great employer who gave me 10 vacations a year. I must say that I threatened to be fired if I did not get time off. Then I started working as a diving instructor. First for an employer. There I had to be retrained as a PADI instructor. During the swimming test, I benefited greatly from all those years of training in the pool. This old man swam the youngsters beautifully. We provided the diving introductions and lessons for Centre Parcs there. So did the Bubble maker for your nephews. What could be better than passing on your passion to the youth?

In addition to the many training dives, you will regularly go on challenging diving trips. What should I keep in mind?

I now run the diving school Decostop.nl. There I mainly provide technical diving courses. During the course I am often asked where they can best put what they have learned into practice. Then I like to invite them to my annual diving trip to Malta. Perhaps the best advertisement for my courses, the level varies from Advanced to rebreather. I have also followed and given many courses on Malta myself. Such as IDC Staff instructor. I also give Trimix courses there, such as the TDI Trimix 75 course specially developed for Malta. There are many cool wrecks around Malta up to 75 meters. Also deeper, but with the current helium prices they can actually only be reached with rebreathers. Besides wrecks, cave diving is perhaps an even greater love. You will find me regularly in the Lot department in France. To give training or to dive myself. As an instructor and Instructor Trainer you have to be well above the material. That is why I can often be found in caves. 

Cave diving is the ultimate adventure for you? 

Yes, in a cave everything just comes together. Of course, a lot of education and training precedes this. When you can explore a new part of a cave, where you are completely on your own, it is nice that you can seamlessly follow the planning you have made. I believe that the dives I make should not be a goal for others. I never post my dive profile, depth or dive time. But I do dive well over 100 meters in some caves. Whereby the dives including decompression obligations take quite a few hours. My diving school is not called that for nothing Decostop.nl. You see a healthy tension and curiosity in students about what lies around the next bend. I had that feeling both on my first and recent cave dive.

What does a cave diving training look like?

A cave diving training starts with a cavern section, diving in the daylight zone. Here you can practice without too many risks. Finally we go a little way into the cave. Still in the daylight zone. Afterwards I often hear from students that there was a healthy tension, usually they are convinced. The next step is then intro to cave. An unfortunate name, because it is not an introduction. Now we are actually going to cave dive. There is also a cave or full cave brevet. The latter is more for greater depths with decompression obligations. With the intro to cave brevet you really go into the cave. During the training we do exercises there. Such as laying lines and placing markers. We also practice various scenarios. How do you act when a dive light fails? What do you do if you lose the guide line? At the end of the training you are also a solo diver. You will have to be able to solve everything yourself at any time during a cave dive. Bring yourself to the exit. 

That all sounds great, what a shame that you can only cave dive nearby in France.

I understand that many people immediately think of Mexico when they think of cave diving. But Sardinia also has caves that have beautiful decorations of stalagmites and stalactites. This spring I was in Italy where I Caves of Oliero have been diving. And don't forget Spain! The world record for cave diving was set in Pozo Azul! Have you seen the impressive documentary Diving into the Unknown Have you seen it yet? This takes place in thePlura cave in Norway. Closer by, in Belgium, you have a number of interesting mines. Of course, a mine is not a cave, but it is overhead diving. A day's drive from the Netherlands, in Budapest, lies the Molnar Janos cave. Every fall I organize a diving trip to this beautiful city. During the day diving under Budapest and in the evening a bite and a drink above ground. How beautiful can life be.

Wait a minute… are you saying I can dive into a cave under Budapest? 

Yes! There are many thermal baths in Budapest and its surroundings. They get their water from thermal springs. The cave system of the Molnar Janos is also a thermal spring, the water is no less than 26 degrees. With a drysuit you are actually glad when you are under the thermocline, then it cools down to a lovely 20 degrees. The cave is somewhat hidden behind an old bathhouse. Next to the bathhouse is a pond with warm water; Lake Malom. A water mill used to be powered from here. The water is 24 degrees all year round. Curious turtles and frogs swim there. Always fun to take a little dive. And we can use it perfectly to practice the first cave diving skills. The water is refreshed three times a day by the flow from the cave. To then flow via a small lock to the Danube. That is less than 200 meters away. With the beautiful Hungarian parliament building on the other bank. So you can walk to the city in the afternoon to visit beautiful buildings or museums. The large heroes' square is also worth it. After a few days of diving in the Molnar Janos you can go to the Kobanya mine as a change. This is also in Budapest.

The Kobanya mine is more of the same as the Molnár János Cave?

The Molnar Janos was formed by dissolved rock, completely different. Very irregular in structure. The Kobanya mine was carved out by people to extract building materials from the limestone. You can still clearly see the chisel marks on the walls. And because it was made by people, there are also some things left behind. The beautifully forged spiral staircase is a 'mandatory' photo moment. It is very special to dive down via a staircase with a railing. Halfway there is a fuse box. The disadvantage is that the mine is a lot colder, 9 to 11 degrees. The complex is so large that you drive through it by car until you reach the location to dive. You can dive in four different rooms. There was even a brewery. The remains of three churches can also be found in the mine. Completely carved out in the shape of a church. If you know your way around a bit, you can also discover an old communist prison. It doesn't take much imagination to know that you would never have wanted to be there.

Are there also possibilities for nice day trips to an interesting mine in our area?

Near Winterberg in Germany are the Nuttlar and Felicitas slate mines. These mines are super cool. With a lot of historical material under water from excavators, trains and forklifts. But also special areas such as the canteen, explosives storage and the pumping installation. A bit too scary? In Ramsbeck you can visit a dry part of the mine. The same machines are there. You go underground with the old train. Then you can imagine where divers float along in the flooded mines.

Do you actually take a camera into the caves? 

I like to take pictures in caves and mines. However, only when I am not teaching a course. Or when the students have passed. As a kind of dessert. In mines I always want something extra in the picture, so that you can also see that it was made by human hands. Focusing is often a challenge. With extra flashes, in addition to the two standard flashes on the camera, you can take special pictures. I often mount these flashes on the back of the model. So that the light that the model blocks is filled in again. You can also beautifully illuminate a location by placing these slave flashes behind an object or hanging them from the ceiling. 

Do you still have time for exciting wreck dives?

Definitely. I dive at least once a year on the wrecks in Malta. Last spring I also dived on the Amoco Milford Haven. An oil tanker off the coast of Genoa. During unloading a fire broke out, after which the ship sank. The wreck lies nicely upright, with the top at 30 meters and the propeller around 84 meters. In addition to our rebreathers we also had underwater scooters with us. An oil tanker does not only sound big, it is big! With a scooter you can scooter around the wreck at deck level. Especially amidships, where large pipes run across the deck, dozens of enormous groupers are hiding. It is wonderful to do a few laps around the bridge, which protrudes more than 20 meters above the deck, on the way up. Of course you can also go inside, via elevator shafts you can go to other floors. To wander through cabins and the canteen there. Another beautiful wreck near Genoa is the U-455, a German U-boat that sticks up diagonally from the mud. A dive on this wreck will give you four hours of decompression obligation due to the minimum depth of 90 meters. Is it worth it? Yes, it is! How many people can visit such a wreck? It is a beautiful piece of history. You can see the propellers and a periscope where you can still read Carl Zeiss in the lens.

You are one of the guest speakers on the weekend of February 1st and 2nd. Your topic is not about cave diving, is it?!

Really! What could be better than talking about my passion at the largest diving fair in the Netherlands. I have so much to tell and show about Budapest. Both about the Molnar Janos and Kobanya mines. I am going to make a great lecture about that. Even if you never plan to go cave diving, you can enjoy the stories and photos from both above and below water. 

Jeroen Bijmans, guest speaker Duikvaker 1 and 2 February 2025

Stage 2, 11:00 am, City trip Budapest, cave diving under the city.