German cave researcher Johann Westhauser was severely injured when he was hit by falling rocks in the Riesending Schachthöhle ("chute cave") near the town of Berchtesgaden in southern Bavaria on Monday.
Westhauser was one of a group of speleologists who discovered the 19.2 kilometer-long cave system in 1995.
Rescuers will have to descend almost 1,000 meters (3,280 feet) to get him out.
While initial reports suggested Westhauser's head and upper body injuries had debilitated him to the extent that he could only be transported horizontally, it now seems he is able to walk.
But a Bavarian mountain rescue team at the site says it could take up to five days.
The incident has raised questions about the safety of cave research. And indeed, it is risky work.
Peter Jäger, an arachnologist who has worked in caves in Asia, knows what it's like when things get dangerous underground. But as he tells DW, cave research is worth the risk.
Deutsche Welle: You often work in caves, mostly in Laos. Why does an arachnologist have to go underground?
Peter Jäger: In caves, biodiversity isn't as high as it is in the jungle, but the species present in caves have a special history and can tell us a lot about the evolution of these animals.
Give us an example.
Together with my colleague Helmut Steiner, I have described nine new species in Laos. Spiders usually have eight eyes, but we found species with eight, six, four, two and no eyes. And we now want to find out how long it takes in evolution for a species to lose its eyesight.
What else is special about animals in caves?
Elongated extremities: the antennae and legs. The significance here is that in a dark habitat, the species can move around better using the sense of touch, and it gives them a higher chance of survival. There are other cave animals, giant arachnids like giant harvestmen, which set records for their size.
Aren't you a little frightened when you work in caves?
No, not at all. When it's over 30 degrees Celsius (86 degrees Fahrenheit) outside, it's nice to be able to work in a cave where it's only 22 or 25 degrees. That's quite relaxing. But you do have to be aware of some dangers, such as rock fall. And you should never enter a cave after a thunderstorm, because water can rise unexpectedly and you could be swept away by a tidal wave. I take such things seriously - I'm not tired of life!
What's the furthest down you have ever been?
Since I'm not a real cave explorer, I haven't been down very far, maybe 200 meters. But we have been in very long river caves that have been washed out over centuries by rivers and streams. The rock landscape there is perforated by underground corridors and caves. They form the habitat for these organisms that have adapted to the caves.
Can you stand in the caves or do you have to crawl?
Some of them have huge halls - more than 50 meters high. But there are some passages that are a lot narrower and you have to ask yourself: do I really want to go through there? Some researchers crawl through on all fours or like a snake - but I don't do that. Not because I'd get claustrophobic, but because I usually say we have probably already found whatever may be on the other side of the passage.
What kind of equipment do you use?
We have really good head lamps. You should always have two of those, in case one stops working. I don't take ropes, because I don't usually rope down from anywhere - I leave that to my colleagues whose job it is to do that. I have other equipment, such like alcohol jars and tweezers.
Are there any safety rules for caves? Divers, for instance, have a rule that you should never dive alone.
Absolutely! You should never go into a cave you don't know alone either. And even if you do know the cave, it's still better to go in with a partner. Things can always happen. You might slip and fall and end up with a broken leg - and if that happens it's good to have another person with you. Another thing is that you should always have a lighter with you to help you detect pockets of carbon monoxide - areas where the poisonous gas has collected - because you could suffocate.
What about the caves that you have been to?
In Laos, you have to be careful because the caves were shot at by the American military [during the Vietnam war] and there could still be unexploded munitions in there, like rusty phosphorus bombs. You have to be alert.
Have you ever been in any dicey situations?
Yes. Once I went into a cave but my colleagues had stopped closer to the entrance. I continued to walk and missed a turn. When I tried to go back, I couldn't remember which turn to take - things can look the same down there. But fortunately I had a compass with me.
Isn't it hard to remain calm in a situation like this?
It's definitely a little frightening. Your heart starts beating faster. But I've made it a habit now to take chalk with me and mark the walls at every turn I take.
Aren't you afraid of being buried in a cave?
There's a tourist cave in Laos, where there's one hall with lots of large fallen rocks. When I was in the cave once, another rock came down. It was probably only a two-kilogram stone, but just hearing that sound gives you a fright. A colleague of mine was in an accident down there. He wanted to crawl down, so his wife could take a picture and fell down a five-meter drop. He almost died - thank God he survived.
Peter Jäger is an arachnologist at the Senckenberg Research Institute and Nature Museum in Frankfurt. He leaves for his next cave expedition in two weeks. This time he's going to Thailand.