The World’s Most Amazing Caves

Humans have been drawn to caves for thousands of years. Here are four of the world’s biggest caves.

Son Doong Cave, Vietnam

Son Doong Cave in the remote(偏远的)forests of Vietnam holds the title of the largest cave in the world. Son Doong is a spreading network of tunnels and caves, the largest of which could contain an entire New York City block with 40-story buildings. Parts of the cave’s top have fallen down，creating vast skylights that allow life to grow to a height of hundreds of feet beneath the forest floor.

Mammoth Cave, Kentucky, the United States

Mammoth Cave in Kentucky is the longest cave system in the world, with 426 miles explored—and scientists guess another 600 miles have yet to be discovered based on measurements of air movement within the caves. Mammoth Cave has drawn visitors since the 1800s, and 10 miles of underground passages are accessible to tourists today.

Sac Actun. Mexico

The longest underwater cave system in the world, Sac Actun winds(蜿蜒)more than 215 miles under Mexico’s Yucatan Peninsula. Adventurers can take a drop in the Sac Actun system through more than 248 cenotes(天然井)—the natural swimming pools that form when sinkholes connect the surface to the underwater caves.

Veryovkina Cave, Abkhazia, Georgia

Veryovkina Cave is the deepest cave in the world, spreading 1.4 miles beneath the surface. It takes professionals a week to make a round journey to Veryovkina Cave, They have to brave waterfalls, tight presses and sharp drops. But the payoff is excellent—Veryovkina

Cave’s end is a beautiful blue lake about 50 feet long and 25 feet wide surrounded by black black rocks.

Have you ever thought of taking a train and having an adventure? Riding the train can be a real adventure. That is how I feel every time I take Amtrak. I often take a four-hour trip to visit my children. Every time I take this trip I never know what will happen.

Last week when I was on the train and over an hour into the train ride, there was a man sitting by himself in the back of the train carrying on a mobile phone conversation — in another language. It was loud and disturbed most of the people on the train. I think it was annoying.

Fortunately I sat next to a wonderful old lady who was taking a two-day trip by train. She said her two daughters were distraught at the thought of her driving for three days to reach her home, although she had no trouble driving. The train ride was the only choice for her. She loved to look out of the window and watch the world go by on the train.

She was fun to talk to and asked me when my children started being parents. That is a very good question. Both of us are old and have children. She asked that same question from time to time.

There are always many people on the train from all walks of life, different countries, and many languages. Riding the train is a great way to increase your knowledge and take in all kinds of cultures. If you get hungry, you can buy food in the food car at any time. If you need to use the restroom there is always one available.

It sure beats driving the car, which has to stop for food and restrooms. And it is better than taking the bus.

Last month I was lucky enough to have a chance to make a trip into space with my friend Li Yanping, an astronomer. We visited the moon in our spaceship!

Before we left, Li Yanping explained to me that the force of gravity would change three times on our journey and that the first change would be the most powerful. Then we were off. As the rocket rose into the air, we were pushed back into our seats because we were trying to escape the pull of the earth’s gravity. It was so hard that we could not say anything to each other. Gradually the weight lessened and I was able to talk to him. "Why is the spaceship not falling back to the earth? On the earth if I fall from a tree I will fall to the ground." I asked. "We are too far from the earth now to feel its pull, " he explained, "so we feel as if there is no gravity at all. When we get closer to the moon, we shall feel its gravity pulling us, but it will not be as strong a pull as the earth's. " I cheered up immediately and floated weightlessly around in our spaceship cabin watching the earth become smaller and the moon larger.

When we got there, I wanted to explore immediately. "Come on," I said. "If you are right, my mass will be less than on the earth because the moon is smaller and I will be able to move more freely. I might even grow taller if I stay here long enough. I shall certainly weigh less!" I laughed and climbed down the steps from the spaceship. But when I tried to step forward, I found I was carried twice as far as on the earth and fell over. "Oh dear," I cried, "walking does need a bit of practice now that gravity has changed." After a while I got the hang of it and we began to enjoy ourselves.