Though they often get passed over for more accessible and well-known attractions, natural and manmade subterranean structures are often more interesting and mysterious than their above ground counterparts.
Whether created by paranoid governments intent on surviving a nuclear holocaust, or by floods, meteorites, or eons of underground erosion, caves, craters, bunkers and lairs are just downright fascinting.
They’re found all over the world, but in this video we’ll focus on ones in America.
Let’s jump in.
1. Greenbrier Bunker, West Virginia
Located amidst southwest West Virginia’s scenic Allegheny Mountains, The Greenbrier is a sprawling luxury resort that for much of the Cold War doubled as a potential last-minute nuclear retreat site for Washington’s political elite.
Most of the original buildings were built more than a century ago by the Chesapeake and Ohio Railroad, but though the resort itself is among the most opulent and exclusive in the region, it hid a big secret that went undetected for decades, which was quite a fete considering the bunker took years to build by hundreds of workers and required thousands of tons of concrete and steel, all of which was delivered by truck.
Spread over more than 100,000 square feet (9,300 square meters) and buried 720 feet (219 m) underground, the bunker under The Greenbrier is about the size of two American football fields stacked one on top of the other.
Design began in the ‘50s and construction got underway in the early ‘60s, but contrary to popular belief, the underground shelter wasn’t designed to withstand a direct hit from an ICBM.
However, at least theoretically it could have weathered a blast as close as 15 miles away, after which it would’ve been able to keep the politicians ensconced inside relatively safe and healthy for years afterward.
Code named “Project Greek Island,” the bunker was large enough to hold more than 1,000 Senators and Congressmen as well as their staffs and families, because who better to lead the nation through post-apocalypse rebuilding than those who failed to stop it in the first place.
The two-story structure featured both private and communal areas and was decked out with state-of-the-art communications, air and water purification systems, generators, decontamination facilities, and enough non-perishable food to last until the proverbial smoke cleared.
It’s not clear whether the Soviets even knew of the bunker’s existence, but since it was nearly 250 miles away from Washington DC – which would have been ground zero in a thermonuclear attack – its 20-ton blast-proof doors were more than adequate.
Thankfully the bunker never had to fulfill the role for which it was built, but during the Second World War it served as an internment center for high-ranking German and Japanese diplomats and captured military brass.
It briefly opened during the 1942 season but was bought – some say against the owner’s will – by the US Army for the paltry sum of $3.3 million (about 50 million USD today) which was well below its market value, after which much of it was converted into a 2,000-bed hospital that opened in late 1943.
After the war the hospital was closed after having housed nearly 25,000 patients, and was resold back to the railroad for the original purchase price.
Then after a multi-year redecoration and modernization project it reopened in 1948, and since then has hosted more than 25 Presidents and Vice Presidents as well as countless foreign dignitaries and heads of state including the Duke of Windsor and Wallis Simpson, Princess Grace of Monaco, and Indira Gandhi.
Though now the bunker is little more than an interesting historic curiosity, the resort, which has more than 700 rooms and dozens of bars, restaurants and shops spread over more than 11,000 acres (4,500 ha), still attracts well-heeled visitors from all over the world.
2. Old Sacramento Underground, California
From December 1861 to January the following year, the central California coast experienced a truly epic Pacific storm, and the state capital of Sacramento bore the brunt of the destruction.
Hammered by more than 40 days of incessant fury, the region was inundated with nearly four times its average annual rainfall, and the effects were felt as far away as the Midwest and even the Gulf Coast states, both of which were embroiled in the American Civil War.
The city and the surrounding areas were deluged with hundreds of millions of cubic yards of water that washed thousands to their deaths and turned the Sacramento Valley into a vast freshwater sea that stretched nearly 300 miles (480 km) inland.
In addition, nearly one million head of cattle were lost, or approximately ¼ of the state’s entire population, most of which belonged to small ranchers.
But though the worst was yet to come, local newspapers declared that Christmas had officially been cancelled, and that in all likelihood the city would never recover.
Less than a month later paddle and steamboats sailed through old parts of the city rescuing survivors from flooded streets that’d once carried automobile and pedestrian traffic, and the state’s newly elected governor had to the travel via boat to the capitol building for inauguration, after which the legislature was moved to nearby San Francisco.
When the water finally receded, the corpses were collected and the damage was assessed, many residents and officials called for the city to be abandoned permanently, lest the tragedy repeat itself.
However, pro-rebuilding voices won the day, and a massive reconstruction project began that would ultimately take nearly two decades, and would result in most of the city being raised between nine (2.7 m) and 14 feet (4.25 m).
Other cities up and down the West Coast had experienced similar storms and floods in the past, though none as large as the one that thrashed Sacramento, and it was the first municipality to attempt the mammoth undertaking of raising its street level, though Seattle to the north would do the same nearly three decades later.
All told thousands of homes and businesses were abandoned, and though many were still used as residences and storage areas in the following years, others were sealed off permanently, turning them into time capsules that wouldn’t be rediscovered until decades later.
The plan to rebuild the city had three central elements.
The area’s rivers would have to be permanently rerouted, levees and dykes would have to be upgraded and reinforced, and nearly all of the downtown area would have to be raised.
Despite abundant naysayers and a total cost that far exceeded a billion US dollars in today’s money, much of the actual work was carried out by private home and business owners and hordes of volunteers determined to return the city to its former glory at any cost.
Though it’s not clear just how big the Sacramento Underground is and how much of it has been rediscovered, it’s likely that in the following decades as the city continues to expand, that even more will be unearthed.
3. Mammoth Cave, Kentucky
Consisting of more than 400 miles (650 km) of mapped passageways, Kentucky’s Mammoth-Flint Ridge Cave System is the largest known subterranean labyrinth in the world – nearly twice as long as the second-longest, Mexico’s Sac Actun underwater cave.
New discoveries and previously undetected connections add miles to this figure each year, hence its name, which has nothing to do with woolly mammoths as is commonly thought.
Anthropologists and archaeologists have found evidence that Native Americans explored the caves as many as 4,000 years ago, but it was probably only “officially” discovered in the late 18th century by local trappers and woodsmen.
Located in west-central Kentucky, the park in which the cave system resides was established to protect the site in July of 1941, and now spreads over more than 52,000 acres (21,000 ha) across three counties.
The temperature inside mammoth cave remains a relatively constant 55 degrees Fahrenheit (12.7 C) throughout the year, and the inside features waterfalls, otherworldly geological formations, flowing rivers and an abundance of animals like blind fish and salamanders, albino shrimp and endangered species of bats that have adapted to the nearly lightless conditions.
The complex network of caves and passageways developed over millions of years as the underlying limestone strata and the sandstone above it were fractured, flooded and eroded repeatedly, a process that is still happening today and making the caves ever larger.
Though most of the uppermost caprock is too hard and dense for water to penetrate, exceptions occur in areas where vertical cracks have formed, hence unlike other caves that are perpetually wet, much of Mammoth Cave is dry, and therefore it has few stalactites and stalagmites which only form in the presence of dripping water.
Much of the water that does find its way into the caves is from natural springs, but more comes from rain runoff at higher elevations which make for dramatic scenes in some areas, like at the Frozen Niagara Room where a waterfall flows for much of the year.
Despite its porous nature and multiple layers, Mammoth Cave is particularly stable which makes it safe for visitors on guided tours, scientists, and amateur spelunkers, the latter of which often resort to clandestine explorations in precarious areas that are technically off limits.
Each of the sedimentary rock layers above the caves are divided into multiple “formations” and further sub-units, but though one particularly dark portion of the cave is commonly referred to as the “bottomless pit,” it’s been found to be only slight more than 100 feet (30 m) deep.
Mapping has been done by multiple methods including physical exploration as well as using ground penetrating radar and sound waves to reveal both solid and open areas, all of which together have provided accurate representation even of areas that may never actually be visited.
The cave was made a UNESCO World Heritage Site in 1981, and an international Biosphere Reserve in 1990.
4. Meteor Crater, Arizona
Located 40 miles (62 km) west of Flagstaff, Arizona, the aptly named Meteor Crater is a massive depression caused by a meteorite slamming into the site approximately 50,000 years ago, though up until the 19th century it was assumed that it’d been caused by a volcanic steam explosion emanating from the San Francisco Mountains (Arizona not California) just 40 miles (62 km) west.
At an elevation of more than a mile above sea level (5,640 ft – 1,719 m) the huge bowl measures nearly 4,000 feet (1,200 m) across, is more than 550 feet (170 m) deep and is surrounded by a rim that protrudes nearly 150 feet (45 m) above the adjacent desert.
Over the years the crater has had various names, most of which were derived from the last names of the men who discovered, studied and owned it, but also due to nearby towns like Meteor, Arizona, and other natural landmarks in the vicinity like Diablo Canyon.
These days Meteor Crater is most commonly referred to as Barringer Crater after geologist Daniel M. Barringer who proposed and later proved that it had been created by an impacting meteorite and not a volcanic explosion nearby.
Shortly thereafter Barringer filed a mining claim for the land around the crater, and his family still owns it today.
It’s thought that the offending meteorite was composed primarily of nickel and iron, that it was ovular and approximately 160 feet (50 meters) across, that it weighed a staggering 100 million tons, and that when it plowed into the earth it was probably traveling between 29,000 miles per hour (12.8 km/s) and 45,000 miles per hour (20 km/s), though as much as half its total mass may have burned off in the atmosphere.
Even so, the resulting energy at impact was calculated to be equivalent to the explosion of a nuclear device with a 10 megaton yield, or more than 1,000 times more powerful than the ones dropped on Japan at the end of World War II.
Other much older meteor craters in various parts of the world are much less preserved due to age and wind and water erosion.
The relatively young age of Meteor Crater paired with the dry Arizona climate have allowed it to remain in nearly pristine condition, but despite attempts to make the crater a public landmark, it has always remained on private land, and as such it’s not protected as a national monument, which would require federal ownership.
However it was designated a National Natural Landmark more than five decades ago, and during the ‘60s and ‘70s was training for the Apollo moon missions.
It has also had its share of mysterious incidents, like one in the mid-’60s when two commercial pilots attempted to fly over the crater in a tiny CessnaHowever as they approached the opposite rim the plane stalled, crashed, and caught fire.
Though badly injured both pilots survived.
It was later reported that the plane ran out of fuel, which wasn’t the case.
In fact the pilots claimed that the stall was caused not by a loss of engine power, but by a lack of sufficient lift under the wings which was unlike anything they’d ever experienced.
A small portion of the wreckage is still visible on the crater’s rim.