1

The horse diaper

Image: Lucia Macedo

Designed to catch manure in crowded cities—a problem once so severe that it shaped public infrastructure as well as the entrances to houses—the horse diaper was an invention meant to be strapped beneath working horses pulling carts and carriages.

The idea was to reduce disease and street filth during the horse-powered urban era. While the device saw limited use before automobiles rapidly replaced horses, similar designs are still occasionally used in modern veterinary practice.

2

The baby cage

Image: Taylor Flowe

Built as wire cages attached to apartment windows, so-called "baby cages" allowed infants to get fresh air when outdoor space was unavailable. Some models were guaranteed to safely hold over 30 pounds.

While alarming today and ultimately abandoned due to obvious safety concerns, the designs likely inspired some of the baby-proofing nets used today.

3

The pneumatic subway

Image: Eddi Aguirre

In the late 1860s, American entrepreneur and inventor Alfred Ely Beach set out to prove the feasibility of a human-sized pneumatic subway system beneath New York City, capable of moving both people and cargo using nothing more than air pressure.

The prototype was set up as a public attraction and carried passengers along a tunnel just over 300 feet long, from a station to a dead end. Despite its initial success, bureaucratic obstacles and high costs halted expansion, leaving it as a functional but largely forgotten underground experiment.

4

The mechanical horse

Image: Gabriel Tovar

Created for exercise and riding practice, the mechanical horse used a system of gears, cranks, and pedals to simulate walking and trotting motions while the rider sat in a saddle-like seat. It was marketed to urban riders and cavalry trainees who lacked access to stables or live horses.

Though bulky and impractical for widespread use, the device anticipated modern fitness machines by replicating real-world movements for conditioning and skill retention, rather than simple repetitive exercise.

5

The first metal detector

Image: Fer Troulik

After a failed assassination attempt on President James Garfield, Alexander Graham Bell hastily built an early metal detector in an effort to locate the bullet lodged in his body. The device functioned as intended, but it was unable to find the bullet because metal bed springs interfered with the signal.

Despite this setback, Bell’s early design proved the concept and directly influenced the development of modern metal detectors.

6

The pet-powered butter churn

Image: Matt Bero

In an inventive twist on animal-powered machinery, some 19th-century American farmers rigged small treadwheels for dogs, cats, or even goats to generate kinetic energy for churning butter. The animal ran inside the wheel, turning a rope or pulley connected to the churn.

While technically functional, the system was limited by the animal's willingness to cooperate and the small amount of power it generated.

7

The umbrella hat

Image: Claudio Schwarz

Robert W. Patten, often called the "Umbrella Man," patented one of the first commercially successful hands-free umbrella hats. It strapped a small umbrella directly to the wearer’s head, providing both sun and rain protection while keeping the hands free for work or walking.

His original design even included a mosquito net attached to the canopy. Patten didn’t enjoy much commercial success but became somewhat of an eccentric and comical popular figure, partly due to a series of comics that were inspired by his unusual invention.

8

The one-wheel motorcycle

Image: CJ Toscano

In 1971, American inventor Kerry McLean built and refined a monowheel—a one‑wheeled motorized vehicle in which the rider and engine sit inside the wheel’s circumference.

Since then, various attempts have been made to build on his original design, but it remains a niche vehicle used primarily for entertainment rather than practicality, as riders must be highly skilled simply to turn or even stay upright.

9

The first talking doll

Image: Holly Ward

In 1890, Thomas Edison embedded miniature versions of one of his most popular inventions —the phonograph—inside dolls so they could recite nursery rhymes.

While the idea was innovative, the technology was not yet there. The recordings were fragile, distorted, and often failed to work properly. The dolls were pulled from the market within weeks due to customer complaints, making it one of Edison’s rare commercial failures.

10

The glass harmonica

Image: Francesco Bovolin

Faithful to his eccentricity and inventive spirit, Benjamin Franklin redesigned the existing glass harp into a rotating spindle of glass bowls, played by touching the spinning rims with wet fingers, which he called the "glass harmonica."

The instrument produced eerie, sustained tones unlike anything else of its era. However, its fragile nature made it somewhat impractical, and the rotating mechanism posed a potential danger to the player if anything went wrong.

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.