100% pure exploration, where you don't know what lies ahead
At a time when the unknown world is disappearing from maps, there is one man who continues to see landscapes never before seen by humankind, as if he has them all to himself: cave explorer Katsuji Yoshida.
"When you're climbing a mountain, you can see the top of the mountain, but with a cave you can't see from the outside, and you don't even know where the entrance is. It's common to start off with an idea that the entrance hole might be somewhere around here, only to find that it's a dead end after 5 meters. Conversely, there are times when a hole you weren't expecting at all leads deep into the cavern and turns out to be a huge cavern. You can't see what kind of world lies beyond it on a map or with the naked eye, and you can't even imagine it. Caves are filled with the absolute unknown, which can only be seen by diving into the hole."
Of course, it's pitch black inside the cave. Communication with the outside world is completely cut off, and there's a constant risk of rockfalls and flooding. People set up camp in such conditions and sometimes stay there for more than a month.
"In caves where there are few living creatures, anything humans bring in could have a serious impact on the ecosystem. We collect excrement in tanks and bring it back to the surface, and if we have to defecate in a place where there are no tanks, we put the contents in an airtight bag and hide it between our helmets and heads. If we put it in our backpacks, the bag gets compressed when we go through narrow passages and leaks. It's a little inconvenient, but once you get used to it, it's fine."
Before I knew it, I had been doing it for over 30 years.
"You see, I don't like caves. I just love the unknown and unexplored world, and I just want to see it. Nowadays, caves are the only unknown and unexplored world, so I have no choice but to do it (laughs)."
As a child, he had a lot of energy and was always fighting. After dropping out of high school and working at a construction site, he decided to take up mountain climbing. Not satisfied with the harsh winter mountain climbing, he tried many outdoor activities such as scuba diving, but nothing really caught his eye. That's when he discovered cave exploration.
"I don't like dark places, and I thought caves were too scary! But I'll never forget the excitement I felt when I crawled through an unnamed hole in Aichi Prefecture and suddenly emerged into a space about the size of a four-and-a-half-tatami mat room. I was shocked by the overwhelming power of the cave, as if the world had suddenly opened up before my eyes. This was what I had been looking for."
30 minutes left to die! The decision made underwater that decided his fate
Since then, I have been exploring nameless caves both in Japan and abroad. Most of these are spaces that humans have never set foot in before. I descend to the underground via a single rope from an entrance that is higher than Tokyo Tower. I also navigate in a packraft through a river inside the cave that may fill with water if it rains.
The passages are completely filled with water, and the explorers have to dive underwater with air tanks on their backs. Cave exploration requires advanced knowledge and skills related to mountains, oceans, rivers, and all other outdoor activities. The fact that it is sometimes done alone makes it even more dangerous.
"Diving is especially dangerous. Your tank or your body gets caught in a narrow passageway and you can't move. At that moment, your mind starts a stopwatch. You have 30 minutes of air left. If you can't escape within that time, you're dead."
You navigate a hole filled with water. Diving in a cave where there is no rescue from outside is extremely dangerous. You are the only one who can protect your life. 
He twists his body as he makes his way through the narrow hole, selfie stick in hand. He puts a lot of effort into taking photos to convey the inside of the cave, which is difficult to describe in words. Yoshida has a huge fear of cockroaches. "I try to choose caves where there are as few cockroaches as possible," he tells me confidingly. 
There are few flat areas inside the cave, making camping difficult. You may find yourself sleeping right next to a gaping vertical hole. If you accidentally turn over in your sleep, you could die instantly. 
For Yoshida, exploration means investigating unknown spaces and publishing the results. When exploring, he always surveys the area and creates maps based on that data. 
Staying in a cave for several days can be extremely stressful both physically and mentally. The menu is carefully planned to ensure mealtimes are enjoyable. At times, over 100 kg of ingredients are brought into the cave to be cooked, including pancakes, sukiyaki, hotpot, and even eggs on rice. Since leftovers are taken home, it's a rule to drink every last drop of ramen soup.
I have felt the presence of death many times in my life, and what I have learned from these experiences is that "humans have choices."
"I have a choice: I can spend the remaining 30 minutes panicking and raging, or I can calmly think of a way to escape and execute it. So it's better to come up with a solution that will allow me to survive in the shortest time possible. Previously, when I got stuck underwater, I knew I couldn't go back, but I could go forward, so I moved forward without hesitation. But I didn't know if there was a place up ahead where I could pop my head out of the water. But I had no choice but to do it. Luckily, I came out into a place with about 2 meters of space between the water's surface and the ceiling, so I got myself ready and headed back. When I returned to where I started my dive, I had no air left. I was lucky to have survived, that's all."
He himself says that "it's not surprising that I could die at any moment," but he still goes into caves because his longing for the unknown outweighs his fear. His next target is a high mountain in a certain country, 3,600 meters above sea level. He will descend about 2,300 meters down a vertical hole into what is believed to be the deepest cave in the world.
"At this very moment, heavy rain could be falling somewhere, washing away the mud inside a cave and creating a path to an incredible space. The underground space is constantly changing, and it's a treasure trove of the unknown and unexplored. When I think about that, I just can't stop exploring caves!"
A trip to a place where you can experience Yoshida's adventures
This cave is located in the Kakino River basin in Yamagata City, Gifu Prefecture. It can only be entered on a caving tour run by Chikyu Tankensha, which Yoshida represents, and involves exploring to reach the underground lake that sparkles with crystal blue light. "There are courses that even beginners can enjoy safely, so if you're interested in caves, I recommend it. However, exploring without a guide is dangerous, so please do not do so under any circumstances," says Yoshida.
