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Join us in this captivating exploration of unknown realms and ancient secrets that lie hidden within these captivating sites.
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00:01There are many myths around arguably the greatest structure ever built by humans, the Great Wall of China.
00:08Some say it's so grand that it's visible from space.
00:13Others claim that you can see it from as far as the moon.
00:17Other theories suggest that the builders of the wall were left inside.
00:22Well, sorry to disappoint you, but all these impressive stories are just myths.
00:29But even with those stories busted, the Great Wall of China is an impressive and truly breathtaking structure.
00:35So let me tell you its true story.
00:38Today, China is one of the most populated countries in the world, counting as many as 1.4 billion residents.
00:46It's also one of the oldest nations in the world.
00:49It has 3,500 years of continuous written history.
00:53But the civilization existed long before that.
00:56There is a theory that while the European continent, for example, was most likely reached by humans from Africa,
01:04China wasn't populated by settlers that came from somewhere else.
01:08Some people believe that the Chinese civilization got formed from local Stone Age people
01:14who lived on the territory since the prehistoric period.
01:17So now, the Great Wall of China.
01:20It's truly big even by today's standard, stretching for over 13,000 miles.
01:26To imagine it better, it's almost five times the distance between New York and Los Angeles.
01:33Or even a bit greater than the distance between the North and South Poles.
01:38Even in modern times, people have never built anything close to this big.
01:43Of course, it didn't take a day to build the Great Wall of China.
01:47Two, keep going.
01:48In fact, the wall was being built for centuries.
01:52Maybe you know that ancient cities had walls around them to protect themselves from invaders.
01:57Yes, Chinese cities had them too.
02:00The first Chinese emperor united the country in 220 BCE and got a brilliant but very ambitious idea
02:07to turn all city walls into one big wall that would defend the country's border against attacks from the North.
02:15A trusted general directed the construction, enrolling a big group of workers, soldiers, commoners, and convicts.
02:23Back then, the wall was built of rammed earth and wood.
02:26In some places that were strategically important, the sections of the wall overlapped to provide maximum security.
02:33The walls were around 26 feet high on average.
02:38But the Great Wall didn't yet look like the construction we know today.
02:42Every next emperor would pick up the big wall project, strengthening and extending it, repairing,
02:48but also modernizing construction techniques.
02:51Some used bricks to build it.
02:53Others moved on to granite and marble blocks.
02:57Watchtowers and platforms weren't there from the beginning as well.
03:00They were added by Ming emperors.
03:03The watchtowers made it possible to communicate with other parts of the wall through smoke and fire messages.
03:09So, the wall is quite inconsistent in terms of material.
03:13But it only adds more charm to the construction and shows how much effort and time it took.
03:19The reason why some parts of the wall have been standing for centuries and are still in good condition is
03:25glutinous rice flour.
03:27Turns out, this sticky rice mortar is almost like cement.
03:32It's very strong and waterproof, sealing the bricks so tightly together that even sneaky weeds can't grow between them.
03:39You may also notice that some bricks have writings carved on them.
03:43They were left by the workers who were building the wall.
03:46The purpose of those writings is quality assurance.
03:50They contain such information as location, quantity, and responsible officials.
03:55So, in the case of some problems with the quality of materials or constructions, it would be known who should
04:01be held accountable for it.
04:04Recently, a research group has looked through official historical documents of the Ming dynasty that ruled China from the 14th
04:11to the 17th centuries.
04:12They came across records of secret doors in the Great Wall.
04:16So, they decided to find them.
04:19They used a flying robot to capture continuous centimeter resolution photos of the wall.
04:25They photographed 90% of the wall that was built during the Ming dynasty and discovered the remains of over
04:31220 secret doors along the wall.
04:35Some of them have a specific width and height that allows only one person to go through.
04:40Others are large enough to allow two horses to pass at the same time.
04:45Why are the doors there?
04:48Well, the Great Wall's main goal was to protect the country from the enemy.
04:53Building doors that could let the enemy in would undermine the whole point of having a wall.
04:58So, of course, the doors were secret passages.
05:01They perfectly matched the surroundings topographically.
05:04And the exit on the outside was camouflaged with bricks so that it was almost completely indistinguishable from the brick
05:11wall.
05:12The wall was never just a defensive wall.
05:15And it was never completely closed.
05:17It could be opened on demand.
05:19It was also a structure used for trade and commerce, communication between inside and outside the wall,
05:25and, of course, for defense and spying.
05:29Some doors were used for trade with the other side.
05:32Through smaller doors, a person would sneak out to spy on the enemy that lived on the other side.
05:39The hidden gates were also useful for a sudden attack.
05:42As you remember, some gates were camouflaged with brick on the outside.
05:47The exit was so indistinguishable that the enemy had no idea exactly where it was located.
05:53The inside entrance for Chinese soldiers was hollow.
05:56So they could walk through the wall and break the camouflaged exit gate from the inside, starting their surprise attack.
06:04Now, even though the main point was to prevent outsiders from getting into the city,
06:09the wall wasn't too effective on that matter.
06:11It could still be climbed over or marched around.
06:15So the wall was being watched at all times.
06:18And the guards gave signals to the troops if they saw the enemy approach.
06:24Also, the wall provided more time to mobilize and bulk up the country's forces
06:28or lure the enemy troops into a difficult strategic position.
06:33The construction stopped at the end of the 19th century.
06:36The wall lost its strategic and military importance due to technological advances.
06:43Over the centuries to today, only 8% of the Great Wall is in good condition, and the rest is
06:49damaged.
06:50Also, around one-third of the wall has disappeared without a trace,
06:55due to both natural erosion and human damage.
06:58I guess you could say it's now just a pretty good wall.
07:01As you remember, the first parts of the wall were built out of rammed earth and wood.
07:06These are not the most unfailing materials if we're talking about thousands of years.
07:12Also, destructive farming methods have turned large areas into a desert and contributed to erosion.
07:19Also, many bricks were taken away from the wall in the last century to be used in building farms and
07:24houses.
07:25The wall is being deconstructed stone by stone even today, but this time by tourists.
07:31Quite a few of them take a stone as a souvenir.
07:34That's a total of a lot of stones, considering that over 10 million tourists visit the Great Wall every year.
07:42Since 1987, the wall has been a UNESCO World Heritage Site, highlighting that it has an outstanding importance to humanity.
07:51The wall is one of China's 56 World Heritage Sites, second place among countries with landmarks protected by UNESCO.
08:00Who's first, you ask?
08:01Well, the top spot with 58 World Heritage Sites belongs to Italy.
08:07And do you know that the wall isn't only a famous tourist attraction, but also the location of the Great
08:14Wall Marathon?
08:16It's a marathon that was established in 1999 and is one of the most challenging ones in the world.
08:22You guessed right.
08:24People run along the wall, including all the steps.
08:27There are three distances, so that participants can run a full marathon that is 26 miles, a half marathon that's
08:3413 miles, or just have a fun run of 5 miles.
08:41Imagine dark labyrinths, deep, deep underground.
08:45They're full of hidden dangers and unexpected discoveries.
08:50Get your flashlight, and let me take you on a tour of the spookiest caves of all time.
08:57And the first destination on our list is Cathedral Caverns in Alabama.
09:03Originally, this place was called Bat Cave, but it was later renamed because of what it looks like.
09:09As you approach it, you can't help but notice its huge entrance, measuring 126 feet wide and 25 feet high.
09:18But this grand entrance is just the beginning.
09:22Inside the cave, there are some of the most beautiful formations nature has ever created.
09:28One of the most famous of them is probably Goliath, a giant 45 feet tall stalagmite with a circumference of
09:36243 feet.
09:39Other amazing sites you might want to visit include a caveman, balancing on top of a flowstone wall, a frozen
09:46waterfall, and a forest of tall stalagmites.
09:57The thing is, the sheer size of the cave is still unknown, and only about 2 miles of it are
10:07mapped and open to the public.
10:08But the cave can, and does, show its dangerous side from time to time.
10:13For example, the directors of the 1984 sci-fi movie, What Waits Below, filmed a lot of scenes in Cathedral
10:20Caverns.
10:22But during the shooting, 17 cast and crew members got carbon monoxide poisoning and had to be immediately taken to
10:29a hospital, barely avoiding serious consequences.
10:33But let's move further to Moaning Cavern in California.
10:38What makes it particularly creepy is the bizarre breathing sound.
10:42It's produced by water dripping through bottle-like openings at the base of the cave.
10:47If a person who's unaware of the nature of this breathing comes close, this ominous respiration might cause them to
10:55steer clear of the place.
10:58On the other hand, these moaning sounds might have evoked curiosity in some adventurous souls.
11:04And usually, it didn't end well.
11:07Researchers have found the remains of more than 100 prehistoric people who fell down the cave's 410-foot chasm around
11:1513,000 years ago.
11:18These days, you can go on a tour around the cave, but no deeper than 165 feet into the vertical
11:25opening.
11:26If you're feeling particularly bold, you can rappel down.
11:31But you'll still have to exit using a gothic-looking wrought-iron staircase.
11:37Be careful not to slip.
11:38It's a long way down.
11:41The next cave we'll visit is ominously called Hell Hole.
11:45You can find it in West Virginia.
11:48It's notorious enough to inspire a few horror movies.
11:53Despite its name, the place is chilly, but no less creepy for this discrepancy.
11:58The average temperature inside the cave is 47 degrees Fahrenheit, which makes it the perfect home for a large variety
12:06of bats and other rare cave-dwelling inhabitants.
12:11In fact, in the winter, the cave accommodates about half of the world's population of Virginia big-eared bats.
12:19These are critically endangered and highly vulnerable creatures.
12:24But it won't stop a chill from running down your spine once you see a cloud of 20,000 squeaking,
12:30wing-fluttering bats.
12:33Bell Witch Cave is a relatively small formation located in Tennessee.
12:39And despite its innocent appearance, it serves as the focal point for an equally fantastic and terrifying story.
12:47According to the legend, in the early part of the 19th century, the farmer and his family suffered from the
12:53mischief of a ghost.
12:55It made a lot of noise at night, ripped sheets from beds, and even physically attacked the farmer and some
13:02of his family members.
13:04Eventually, the farmer passed away, and a vial with unknown black liquid was found next to him.
13:10Some people believed that the ghost had somehow poisoned him.
13:15Soon after that, the spirit left the farmer's family alone.
13:21Locals were sure the ghost had returned to a cave near the farm.
13:24They also believed the mystical creature promised to return when the time was right.
13:29Even today, local inhabitants report strange occurrences happening around the cave.
13:35They swear they are linked to the ghost, once taunting the farmer's family.
13:40I bet that no matter how skeptical you are, the cave will make your skin crawl.
13:46And this is Wind Cave in South Dakota.
13:50At first glance, it might seem that there's nothing super scary about this cavern.
13:55No roiling mass of bats, no ancient remains or toxic gases.
14:01But the cave is home to a blood-chilling and very rare geological feature.
14:07Nowhere else in the world will you find a more extensive network of boxwork calcite.
14:14How did Wind Cave create the perfect conditions for the boxwork remains?
14:18It's still a mystery.
14:20But what you do notice is that this boxwork resembles a massive spider web a bit too much for comfort.
14:27Even though it's just a geological anomaly, it's hard to look at the boxwork and not imagine tons of cave
14:34spiders skittering along those thin strands of hardened minerals.
14:39Now, let me take you to a place that seems to be out of this world.
14:45There's nothing mysterious or dangerous about this place, but it's kinda unique.
14:51Life inside this cave has been isolated from the outside world for about five and a half million years.
14:57And it does show.
15:00See for yourself.
15:02Because of such long isolation, the conditions inside Mobile Cave are like nowhere else in the world.
15:09Despite a severe lack of sunlight inside the cave and the toxicity of the air, a unique ecosystem is flourishing
15:17there.
15:18The cave is located a few miles west of the Black Sea in Romania, and it was first found in
15:241986.
15:26These days, you can only visit it if you have special permission.
15:30But even if you have it, the central caverns are guarded naturally, by super-narrow limestone tunnels and vertical shafts.
15:39So, those who are familiar with claustrophobia shouldn't enter this place.
15:45In the depth of the cave, the air has twice less oxygen than the air outside.
15:51It contains a lot of carbon dioxide and hydrogen sulfide, which means it's not the freshest air you can breathe.
15:57It's also pitch black inside the cavern.
16:01But despite, or should I say, thanks to, this cocktail of extremely harsh conditions, the site is a true goldmine
16:09for biologists.
16:10Life seems to be booming here.
16:12In a 1996 study, scientists identified 48 species living there.
16:1933 of them are unique to the cave.
16:21Most of the creatures inhabiting the cave are tiny.
16:25They have long limbs and antennae.
16:27Helping them navigate in the dark.
16:30They also have no vision and lack pigment, which makes sense.
16:35Why would you need to be able to see if you live in total darkness?
16:38And why would you need to be pretty and colorful with no one to see you?
16:43Now, get ready to explore one more cave.
16:46No less amazing, but very different.
16:49This is the giant crystal cave, a.k.a. Cave of the Crystals, in Mexico.
16:57These massive crystals were found in 2000 by a mining company after the water was pumped out of the cave.
17:04Two miners then entered the drying cave on foot and saw the crystals.
17:08These awe-inspiring crystals are actually massive gypsum pillars hidden 984 feet underground.
17:16Scientists estimate that the crystals could have been already growing for half a million years.
17:21That's why many of them are so long and wide that you can walk across them.
17:27Unfortunately, visiting this wonder of nature is impossible at the moment.
17:33But maybe it's for the better, since giant crystal cave is a dangerous place that can easily turn into a
17:39trap.
17:41For tens of thousands of years, it was filled with groundwater,
17:45which was originally pushed upward into the opening by a magma chamber located in the depths of our planet.
17:51The magma under the cave kept the water hot.
17:54But eventually, the temperature of the water dipped below 136 degrees Fahrenheit.
18:00As a result, the water started to fill with calcium and sulfate,
18:05whose particles began to recombine into gypsum.
18:08And then, white-tinted crystals took over the cave.
18:12And since they stayed underwater, they were able to keep growing.
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