 Welcome to Spotlight Advanced. I'm Adam Navas. And I'm Liz Wade. Spotlight uses a special English method of broadcasting. It is easier for people to understand, no matter where in the world they live. A team of people stand in near darkness. The only light comes from the lights attached to the hard helmets on their heads. They are trying to decide what to do. They have been exploring deep under the ground. The cave they are traveling through has become smaller and smaller. They are about to go deeper into the cave than anyone has gone before. They make sure they have power for their lights. The first person must move like a snake to get through the small spaces. He must bend his body into strange shapes to move around the rocks. He does not know if the cave will get smaller around his shoulders. He may need to go back at any moment, but there could be no room to turn around. But suddenly the space grows wider. The person calls back for the rest of his team to follow. He has found a beautiful cave. He starts to set up lights. They shine on a lake of beautiful green water and amazing rock formations. His team joins him. They stand in silence and awe as they all look around at something that no other person has ever seen before. Today's spotlight is on exploring the world's deepest caves. People have used caves for thousands of years. Caves were humans' first shelter from weather and wild animals. People stored food in caves. Today people use caves less as homes, but in some places people do still live in caves. Caves are often naturally cool places, so people still often use caves to store things that need to stay cool. People also dig for rocks and minerals in caves, and some cities even get their water from caves. But caves used this way are near the surface of the earth. Some caves are much, much deeper inside the earth. These caves are less useful. In fact, exploring these deepest caves is not about shelter or storing things. It is about discovery. Carlos Edmundo Cortezoría is from San Luis Potosí in Mexico. He has been exploring caves for more than 10 years. He explained to the website Great Big Story. I love going back down into deep caves that I've been to before. It is always a new experience. It is always different. It is like opening doors to the unknown. And for me that is very fulfilling. All caves are different. You find different things in each. It is something I do every day. I connect with nature, with the caves. I get to know places that almost nobody has been to. I have been doing this for many years now. I like it a lot. There are caves in every part of the world. Many of these caves connect through cracks in the underground rock. They form connected cave systems. There are cave systems in every part of the world, including China, Mexico, Europe, Central America, and North America. Imagine a mountain so tall, it seems to touch the sky. Now imagine people living next to that mountain, but never knowing about it. This seems impossible. But this is what it is like to live near a very deep underground cave. Many of the world's caves go down into the earth, farther than mountains go up. People walk right on top of them, but never go into them. Many people do not even know they are there. Part of the reason for this is because exploring a cave is very dangerous. It has all the dangers of climbing a mountain, but in the dark. A helicopter could rescue someone off a mountain, but there is no similar way to rescue someone in a cave. There are many risks in exploring a cave. One big risk is falling. Sometimes caves go straight down. The only way to enter them is to drop down on ropes for hundreds of meters. If something goes wrong, these falls can kill a person. There is also a risk of being hit by a falling rock. Caves also get very cold. People must prepare for the cold. If they do not, they can suffer hypothermia. When a person has hypothermia, her body is dangerously cold. She may stop moving or thinking well. The risks that may frighten people the most are the risks of losing light or getting lost. But people can avoid these risks by being well prepared and careful. Experienced cave explorers know how to bring extra batteries for lights. They never explore a cave alone. And they know how to be careful about how far they go. But there is one kind of cave that can frighten even experienced cave explorers. River Caves. The country of Slovenia has some of the world's largest river caves. The Rika River drops into the earth. But it does not end. Under the ground, it continues to create caves and lakes. 38 kilometers later, the river comes back out of the ground in Italy. Katrina Kosic Vico is a Slovenian cave explorer. She told National Geographic, River Caves are amazing because they let the visitor go underground and float the lakes and giant rivers. He goes where the sun does not shine. He can observe the amazing power of water in action. He can see aquatic cave animals in their natural environment. And he will enjoy the beauties of cave formations at the same time. People and caves have a long history. Caves are places of safety, but they also are frightening places. The deep darkness of the caves connects to our deepest fears. Fears of being lost. Fears of being alone. Fears of the unknown mystery. People both want to explore caves and are frightened to enter them. But we know that even after people have mapped every square meter of the earth, we have only touched the surface. There is another world just below our feet. What about you? Are there caves near where you live? Would you like to explore them? Tell us what you think. You can leave a comment on our website or email us at radio at radioenglish.net You can also comment on facebook at facebook.com slash spotlight radio. The writer of this program was Adam Navas. The producer was Michio Ozaki. The voices you heard were from the United States and the United Kingdom. All quotes were adapted for this program and voiced by spotlight. You can listen to this program again and read it on the internet at www.radioenglish.net This program is called Exploring Deep Caves. Visit our website to download our free official app for Android and Apple devices. We hope you can join us again for the next spotlight program. Goodbye.