1

Area 51

Image: Michael Herren

Location: Nevada

Shrouded in secrecy, this military base has become synonymous with UFOs and government cover-ups. Its official purpose was testing aircraft like the U-2 spy plane and Stealth Bomber, but its classified nature fueled decades of wild speculation, ranging from secret weapons to actual aliens working for the government.

2

Coral Castle

Image: Audric Wonkam

Location: Florida

This massive stone structure was built by a single man, Edward Leedskalnin, using enormous limestone blocks—some weighing 30 tons. According to him, no heavy machinery was ever used during the construction, and he even claimed to know the secrets of the pyramids . To this day, engineers and historians debate how he moved and placed those stones with such precision.

3

Skinwalker Ranch

Image: Jacob Padilla

Location: Utah

This 512-acre property has long been at the center of UFO sightings, cattle mutilations , and alleged portals to other dimensions. The stories were so compelling that, in the ’90s, a private research organization purchased the ranch to try and make some scientific sense of the claims, conducting extensive field studies. However, after nearly a decade of research, they found no conclusive evidence.

4

Mammoth Cave

Image: Ksenia Kudelkina

Location: Kentucky

The world’s longest known cave system has its fair share of unexplored tunnels, ghost stories, and strange air currents. More than 400 miles have been mapped , yet many passages remain uncharted. Researchers have yet to fully understand the cave’s underground ecosystem, and new chambers are still being discovered today.

5

The Marfa Lights

Image: Alexandra Vo

Location: Texas

Reported since at least the late 19th century, floating orbs of light have been seen near this small town with no consistent explanation. Night watchers continue to gather at designated viewing areas along Highway 90, hoping for a glimpse. While scientific studies suggest that distorted car headlights are the most likely cause, many remain convinced otherwise.

6

The Devil’s Kettle

Image: Andrew Ling

Location: Minnesota

This unusual waterfall splits in two—one half flows normally, while the other vanishes into a deep pothole with no known exit. Scientists poured dye, ping-pong balls, and even GPS trackers into the mysterious hole, all to see where the water ends up. While researchers eventually confirmed it rejoins the river underground, exactly how and where remained elusive for decades.

7

Cahokia Mounds

Image: pcrm Dorego

Location: Illinois

Built centuries before Columbus arrived in the Americas, the ancient city of Cahokia featured massive earthen mounds, wooden palisades, and likely formed part of complex trade networks across the continent. Despite having a population rivaling London in the 1200s, according to archaeologists, the city was mysteriously abandoned in the span of a few years. No written records explain its decline, though environmental stress, resource shortages, and internal social factors are often cited as possible causes.

8

Blythe Intaglios

Image: Alexander Schimmeck

Location: California

Similar to Peru’s Nazca Lines, these giant geoglyphs are etched into the desert floor, seemingly visible only from the sky. Created by scraping away dark rocks to reveal lighter earth beneath, the figures are believed to be between 450 and 2,000 years old, depending on the specific design. While their exact purpose remains a mystery, they are believed to have had a ceremonial function.

9

The Spooklight

Image: Ben Griffiths

Location: Missouri-Oklahoma Border

Also known as the Hornet Spooklight, this floating orb has been seen since at least the late 19th century. It appears along a rural stretch of road near the small community of Hornet, Missouri, and Quapaw, Oklahoma. While some theorize it could be caused by car lights from miles away, some sightings predate automobiles.

10

Roanoke Island

Image: Stephen Crane

Location: North Carolina

In the 1580s, an entire colony vanished overnight, leaving behind only the word "Croatoan" carved into a tree. No graves, no remains—just an eerie disappearance that sparked centuries of theories, from disease and starvation to assimilation with local tribes. Modern archaeology uncovered European artifacts at sites associated with Native groups miles away, but no definitive evidence has ever solved the mystery.

1

What are bills made of?

Unlike other currencies, dollar bills are not made of paper or plastic. U.S. dollar bills are made from a special fabric blend composed of 75% cotton and 25% linen. This mix makes the bills extremely durable and resistant, and they can be folded about 4000 times before tearing.

2

What bills are valid?

Any U.S. dollar bill that was legally printed is valid, no matter how old, as American currency does not have an expiration date. While some bills might not be accepted by businesses of foreign exchange services due to their condition or if they are a discontinued version of the bill, the bills themselves are still valid, and American banks will accept them, though they might take them out of circulation.

3

American leaders

Five bills have a depiction of an American president. The exceptions are the $10 bill, with Alexander Hamilton on the front, and the $100 bill, with Benjamin Franklin. The $1 bill, depicting George Washington, is extremely symbolic: several elements are repeated 13 times as a nod to the thirteen colonies, and it showcases the Bald Eagle and the Eye of Providence as a sign of God watching over America.

4

A change in size

Did you know that dollar bills used to be so big that they were nicknamed "horse blankets"? Original dollar bills were 7.4 × 3.1 inches. In 1929, the Treasury Department reduced the size of bills to 6.14 × 2.61 inches to reduce production costs and materials. Old bills, though still valid, are worth much more as collector items.

5

Uniformity

Besides their value and design, all dollar bills have the same size (6.14 × 2.61 inches), color, and weight (1 gram) , which sets American currency apart from other countries where bills of different values are differentiated by size, color, or both. Why doesn’t the U.S. implement differences among bills? The cost of adapting vending machines, bank drawers, and ATMs to new bill sizes would cost billions of dollars.

6

Hard to copy

Originally, dollars were not green, but black. As time passed, green ink was favored, as it was cheap and did not fade as much as black. The new color also prevented people from using black-and-white cameras to create counterfeit money. Currently, dollar bills are predominantly green, but newer versions also include extra colors, such as pink, orange, or purple.

7

A $100,000 bill?

Have you ever seen a $500 or 1,000 dollar bill? What about a $100,000? Up until 1945, the U.S. Treasury printed $500, $1,000, $5,000, $10,000, and $100,000 notes , in addition to the values currently in use. These higher-value notes were mainly intended for bank and government use, but were sought by criminals as they made it easier to hide large amounts of money. Even though they were officially discontinued in 1969, these notes are still valid, though rare, and they have a high worth as collector's items.

8

No numbers

Unlike bills, American coins have different sizes and colors related to their value. Originally, gold, silver, and copper were used for coins, but modern coins are made of copper, zinc, or nickel. Besides their size and design, the value of each coin is printed in letters, not in numbers , alongside depictions of American presidents.

9

Liberty for all (the coins)

By law, all American coins must include six specific details : the word ‘Liberty’, the name of our country, the national motto "In God We Trust", the oldest American motto "E Pluribus Unum", the value of the coin, and the year. Each coin also includes a mint mark that shows where it was made: "P" for Philadelphia, "D" for Denver, "S" for San Francisco, and "W" for West Point.

10

A global currency

The American dollar is one of the most powerful currencies in the world, acting as a backbone for international trade and finances. It is estimated that two-thirds of the physical dollars in circulation are outside American territory. Besides the U.S. and its territories, eight sovereign nations have the U.S. dollar as their official currency, with several more accepting it as legal tender.

1

There's an unexplained billion-year gap

Look closely at the canyon walls, and you'll notice something strange: a clean, sharp line where ancient rock simply stops, and a much younger layer begins directly above it.

This geological puzzle is called the "Great Unconformity," and it represents over a billion years of rock layers that are simply absent , as though that stretch of time never happened. In some spots, rock dated 1.8 billion years old sits directly beneath rock that is only 520 million years old. Where did the missing billion years go?

The leading theory involves the violent breakup of an ancient supercontinent, but scientists are still piecing it together.

2

During the Cold War, it hid a nuclear fallout shelter

During the Cuban Missile Crisis in 1962, the U.S. government converted part of the Grand Canyon Caverns into a fallout shelter. This dry cave system, more than 200 feet underground, was stocked with enough food and water to sustain 2,000 people. Naturally, it was never occupied, and the supplies were never used.

The caverns have since been transformed into a tourist attraction, with organized tours winding through the same underground chambers that were once intended as a refuge from nuclear war. You can even book a night's stay there.

3

The Federal Aviation Administration was founded after a crash over the canyon

In 1956, two commercial passenger planes collided in midair over the eastern Grand Canyon, killing all 128 people on board both crafts. Rescue teams struggled to reach the wreckage deep inside the canyon, and the extreme heat of the crash had caused the planes' aluminum to fuse with the bedrock. There were no survivors.

The disaster exposed a terrifying truth: the U.S. air traffic control system was dangerously outdated, relying on pilots' visual estimates and rough guesswork from controllers , with no way to separate fast-moving aircraft from slow ones, or instrument-flying planes from those navigating by sight. Congress responded by passing legislation that created both the Federal Aviation Administration (FAA) and the National Transportation Safety Board.

4

A hoax suggested that an Egyptian civilization had lived there

In 1909, the Arizona Gazette reported that an explorer named G. E. Kinkaid had discovered a vast underground citadel inside the canyon, filled with artifacts linked to ancient Egyptian civilization. He even claimed the expedition had been funded by the Smithsonian.

This story described hieroglyphics on the walls, mummies in the chambers, and relics pointing to a direct connection with the Egypt of the pharaohs. It was incredibly detailed, and it was, of course, a hoax. No evidence for any of Kinkaid's claims ever surfaced.

5

Fewer than 100 people have ever hiked its full length

Among the few people who have completed the through-hike of the Grand Canyon is Jen Hogan, the first woman to accomplish it, finishing her journey in 2021–2022.

It’s a full 800-mile length below the rim. The route involves extreme heat, flash floods, near-impassable areas, and stretches with no water or trail whatsoever. Around 60 or 70 people have reportedly accomplished it. This makes it one of the most exclusive feats on Earth.

6

The Grand Canyon's rocks predate dinosaurs entirely

Visitors scanning the canyon walls for fossils are often surprised to learn they won't find any dinosaur bones here. The rock layers of the Grand Canyon are simply older than dinosaurs. This fact alone can be shocking: staring at its walls means staring at marine fossils from as far back as 1.2 billion years ago. Some of its caves hold the remains of ancient mammals. The canyon is a window into a world that existed long before the dinosaurs, when the land that is now Arizona lay beneath a shallow sea.

7

The park is bigger than Rhode Island

Numbers alone rarely capture the Grand Canyon's scale, so here's a different approach. Rhode Island covers about 1,214 square miles, and the Grand Canyon National Park spans 1,904 square miles.

The canyon's depth exceeds four Empire State Buildings (which is 1,454 feet) stacked on top of one another. That’s 6,093 feet at its deepest point.

8

But it's not the deepest canyon on Earth

For all its grandeur, the Grand Canyon does not hold the depth record. Pictured above, the Yarlung Tsangpo Grand Canyon in Tibet, China, plunges to 17,567 feet, which is nearly three times deeper. Carved by the Yarlung Tsangpo River as it cuts through the eastern Himalayas, that canyon is so remote and extreme that it remained largely uncharted until the late 20th century.

9

It is home to a pink rattlesnake found nowhere else on Earth

The Grand Canyon Pink Rattlesnake has a pinkish-red coloring that matches the canyon's own distinctive rock walls so closely that it's nearly invisible. It is found nowhere else in the world. Officially classified as Crotalus oreganus abyssus , it has darker diamond-shaped markings along its back that deepen the camouflage further.

10

There's a village at the bottom: Supai Village

For over 1,000 years, the remote village of Supai has been home to the Havasupai Tribe, the People of the Blue-Green Waters. It is located an eight-mile hike from the rim, but sits roughly 3,000 feet deep inside the Grand Canyon.

The U.S. Department of Agriculture has called it the most remote community in the contiguous United States, and it has no automobiles and no road access. The only ways in are on foot, by mule, or by helicopter. It is also the only place in the United States where the postal service still delivers mail by mule train.