On the territory, in the state of San Luis Potosi, located unique place- Cave of Swallows (Sótano De Las Golondrinas or Cave of Swallows). It is the world's largest karst sinkhole, which is the dream of extreme lovers, tourists and many scientists.
Description of the Swallow Cave
The grotto is often called the 13th wonder of the country, as it is impressive in size - it can easily fit the famous Chrysler Building, located in New York. In its shape, the Swallow Cave resembles a cone-shaped pit expanding downward, the depth of which varies from 333 to 376 m. Researchers suggest that the volume of space inside is 33110 cubic meters. m.
The hole of the hole on the surface of the earth has the shape of an ellipse with a width of 49 m and a length of 62 m. At the bottom it resembles an oval, while one side of it is absolutely flat. The bottom and passages of the Swallow Cave are practically not studied at present.
Where did the name of the grotto come from?
Initially, the aborigines called the attraction Akusmon, which in translation from ancient language Aztec translates as "clean well". When the conquistadors arrived in Mexico, they noticed above the Swallows or flying swifts.
The colonialists named the grotto Golondrinas, which literally can be translated as "basement of the swallows". It is also home to Mexican Arabians and Black Swifts. Every morning the birds fly to the surface of the earth in a spiral, and in the evening they return in the same way. They dive in flocks of several dozen birds until they reach their nests. Most tourists traveling in Mexico tend to get to the Swallow Cave in order to see and take a photo of this magical action.
Exploring the sights
The grotto was first explored in 1966. The study was carried out by Texas scientists led by the world-famous speleologist - Lorenzo Gallardo. They hypothesized that the sinkhole was the result of a fractured roof formed by water erosion.
In and around the Cave of Swallows, a variety of animals, characteristic of the subtropics, live. Here you can find monkeys, deer, squirrels, raccoons, possums, badgers and a variety of reptiles. The flora is represented by ficuses, oaks and strawberry plants. By the way, they grow only in the upper part, and at the bottom, thanks to the coolness, the grotto is covered with mosses and mushrooms.
What is famous for the Swallow Cave?
The sinkhole, together with the surrounding area, is a protected natural. The country's government closely monitors the local ecosystem. There is a huge amount of guano inside the cave, which is the reason for the spread a large number bacteria, so you can only be here in special oxygen masks. Bird droppings also attract snakes and insects.
In order to preserve the ecological complex of the Swallow Cave, descent into it is allowed only from one side. Near the entrance there are anchors that allow you to go down on alpine equipment in 20 minutes. If you are in good physical condition, the ascent will take about 2 hours. It should be borne in mind that the walls in the grotto are slippery and wet, and the air is filled with not the most pleasant smell.
Features of the visit
It's not hard to guess why Swallow cave received such a name. Thousands of these nimble birds have made this cave their favorite place, and there are more than one thousand such feathered inhabitants of the cave.
How to get to the cave of swallows?
Swallow cave located in the Mexican state of San Luis Potosi. You can get there from Mexico City. The flight to Mexico City itself will cost about 30 thousand rubles, plus the registration of a Mexican visa is about 10 thousand. Flight Mexico City - San Louis - Potosi about 15 thousand.
The uniqueness of the swallow cave in Mexico
The Swallow Cave is the second deepest cave in Mexico. The cave attracts speleologists from all over the world with its unusual structure and mystery. The depth is 375 meters. From above, the cave looks like a bottomless black well. Inside the cave has many different passages and manholes, which to this day remain poorly understood and stimulate adventure lovers and experienced cavers to new discoveries.
Too large influx of tourists negatively affected the life of the feathered hosts - swallows, so it was decided to determine the time of visiting the cave when there are no birds in it. The descent can be done from 12 noon to 16 noon. This was done for the safety of the tourists themselves, making the descent, since a collision with a bird can lead to fatal consequences.
Be careful!
It is important to remember that the cave is not only filled with cute swallows, it is a habitat for many species of snakes, spiders and scorpions, so descending into the cave without special clothing can be extremely dangerous. You can go down to the cave of swallows by parachute. This is truly a mesmerizing action for those who love extreme views sports. But this activity is too dangerous for inexperienced jumpers. Such a jump should be calculated in seconds, since untimely opening of the parachute can lead to the fact that you simply collide with the wall of the cave and may die. The free flight time to the cave is 7 seconds.
One descent into the cave by cables takes almost 2 hours, so it can only be carried out by people who are physically prepared for this.
What else to see in San Luis Potosi?
In addition to visiting the cave of swallows, in San Luis Potosi you can take a fascinating walk through the city itself, which is rightfully considered one of the the most beautiful cities Mexico, thanks to its unusual architecture. The city is famous for its beautiful San Francisco Park, central square Plaza del Carmen, which houses the delightful Baroque Iglesia del Carmen church.
They talk about one of the most amazing places on the planet - the Cave of Swallows. The cave is located in the state of San Luis Potosi in Mexico. It is so called because at its bottom there is a colony of thousands of swallows, where they build their nests and raise chicks. The cave is very difficult to see among the forests, so it is extremely difficult to reach it on foot. Usually tourists are taken to the cave in specially equipped jeeps by local residents.
The Swallow Cave is considered the most beautiful in Mexico. Its depth reaches 380 meters - for comparison, a hole of such depth will fully fit the Chrysler Building in New York!
When the cave became popular with tourists, locals worried that crowds of travelers could cause migration or even death of birds. However, later, a strict visiting regime was introduced for the "swallow house" - from 12:00 to 16:00, when the swallows fly away from their nests to hunt insects.
The cave of swallows resembles a bottle in shape: the diameter of the "neck" is approximately 50 meters, becoming wider in depth, and thus increasing up to 160 meters in diameter. By the way, this very fact - despite all the danger - is of the greatest interest among cavers and base jumpers from all over the world!
To descend into the cave, you need to have good physical fitness, since the walls are wet and slippery and have many ledges on which you can easily slip. Professionals conquer the Swallow Cave in about half an hour. However, the most difficult thing is to scramble back, on average, the ascent takes from 2 to 5 hours. A free fall with a parachute lasts about 12 seconds.
However, any extreme sports are allowed to try there only when the birds' nests are empty, since a collision with a flock can lead to the fact that both sides are likely to suffer.
Mexico. Leap into the Swallow Cave.
In the rainforests of central Mexico, there is a huge pit more than 300 meters deep. The cave expands towards the base. Because of the birds that live in the cave, it is known as the Swallow Cave. 
In depth it is the 2nd most deep place in Mexico, and 11th deepest in the world. It is the depth of the cave that attracts many tourists and especially fans of such extreme sports as base jumping (skydiving from any heights). The depth of this cave is from 330 to 375 meters - the entrance is located on a slope and the floor in the cave itself is also inclined. 
A person without a parachute would fall for approximately 12 seconds, from the top of the cave to the bottom of the cave. 
As a result, many extreme enthusiasts take up the challenge to jump off the edge of the cave. There was also a case where an air balloon medium-sized cave was led from the bottom of the cave through its 45-meter entrance.
The cave also popular place for experienced cavers. Descent to the bottom of the cave can take about 20 minutes. Descend there by rope. But the way back is a real challenge to your powers! 
The cave explorer has to climb a single rope using the clamps, which is very tedious. This is a minimum of 40 minutes of tremendous stress, even for highly trained cave explorers it is a serious challenge. And for normal, physically fit people, the journey takes about two hours. 
There is also a psychological point here: the height of the cave is not the only problem, the width makes it much lighter and looks smaller than it actually is. Our brains cannot accurately estimate real distances. Therefore, the climber forces himself to work hard without any visible progress. 
The Swallow Cave has many gentle slopes and stepped transitions. So descending, and even more so to climb the slopes, is a difficult task.
The floor of the pit is covered with the excrement of millions of birds. This excrement, rainwater, and debris from the surface is the food base of the numerous animals on the cave floor. There are centipedes and insects, snakes and scorpions. The air is filled with odors, fungi and bacteria. It is possible to be at the bottom of the cave without a breathing mask, but cavers who wish to explore the far corners of the cave must bring additional equipment with them. 
In the past years, the cave has become a kind of Mecca for jumpers, parachutists and corporate teams. Which is pretty good for local residents who have had no other income until now than Agriculture... They do not even have the usual permanent road to the village, but only a single trail track suitable for jeeps. But the increasing number of visitors is also creating a pollution problem.
In order to protect nature, the cave and its unique ecosystem, the cave explorers agreed to use only one descent point. This place is equipped with rope bolts. Another point is the time of day, the birds fly out of the cave in the morning and arrive in the evening. Cave explorers and especially base jumpers should not disturb the peace of the cave at this time of day.
You can endlessly admire the ingenious creations of nature. One of these amazing places is cave of Swallows... It is located in the Mexican state of San Luis Potosi and is considered the deepest cave in Mexico.
The Swallow Cave can be reached by bus from Mexico City or Monterey in about 5 hours. The bus ticket costs about $ 30.
You can get to the cave along a dirt road, which can only be driven by off-road vehicles.
When we first saw the cave, it didn't seem too big to us. But in reality it is just huge. The shape of the cave resembles a giant bottle: a vertical "neck" with a diameter of 55 meters expands to 140-160 meters. Its depth is whole 376 meters away! For comparison, one of the New York skyscrapers can be hidden in it.
The people who inhabited this area knew about the existence of the cave for a long time, but the first documentary studies were made here only in December 1966.
The Swallow Cave is home to many colonies of not only swallows, but also other birds, including parrots.
In the morning, millions of birds fly out of the cave and rapidly rise to the sky. And with the onset of evening, you can watch how the birds return to the cave and fall like a stone inside. It is a very impressive and unforgettable sight to watch how birds, like stones, fall right into the abyss of the cave and stop near their nests.
You can go down inside the cave with the help of climbing equipment or by parachute. Near the cave, there is a special area for attaching equipment. Descent into the cave with a parachute takes only about 10-15 seconds. In order not to disrupt the usual life of birds, as well as for the safety of people, descents are allowed strictly from 12 to 16 hours, at which time the birds fly away to feed.
Jumping or going down a cave is one thing, but climbing up an almost vertical wall is quite another. The way up takes a couple of hours on average and requires excellent physical fitness.
It's pretty cool in the cave itself. There is vegetation only near the entrance to it. After heavy rains, streams appear, which cascade into the cave. Inside the cave, in addition to birds, many other animals live: various insects, including scorpions, snakes. So inside you need to be extremely careful.
Smells inside, to put it mildly, not very. The air is filled with smells of decay and mold, so being in a cave for a long time without oxygen equipment or special filters is not only unpleasant, but also dangerous.
At the bottom of the cave there is a thick layer of stones and bird droppings. The seabed is sloped and has many small tunnels and splits leading to lower levels. Now they have not yet been fully studied by scientists.
It is noteworthy that part of the filming of the famous film Sanctum took place here.
The dimensions of the cave are really impressive. For the descent and subsequent ascent to the top, you need good physical (I repeat) and moral preparation. If you doubt your abilities, then you can not go down, but just look in the evening at the huge flocks of birds returning to their nests.
