1

The Beale Ciphers - Virginia

In the early 1800s, three coded papers surfaced, said to reveal the location of a hidden treasure in Virginia . Only one cipher (the second) has been partially decoded using the Declaration of Independence, pointing to a stash of gold, silver, and jewels.

Treasure hunters and cryptographers have tried for decades to crack the remaining ciphers. Yet, so far, no one has succeeded.

2

The Georgia Guidestones - Georgia

Erected in 1980, the granite monument carried inscriptions in multiple languages , laying out guidelines for humanity’s future. The massive slabs earned the nickname "America’s Stonehenge."

The mystery lies in who commissioned it. The sponsor used a pseudonym and never revealed their identity. Too bad they were destroyed in 2022 after being damaged by an explosion.

3

The "Wow!" Signal - Ohio, 1977

One night in 1977, Ohio State University’s Big Ear telescope picked up a deep-space radio burst lasting 72 seconds . Astronomer Jerry Ehman circled it and wrote "Wow!" beside the data.

The signal has never been definitively explained. Whether it was a passing comet, a reflection, or something else, no one knows.

4

Roanoke Colony’s "CROATOAN" - North Carolina

In the late 1500s, settlers on Roanoke Island disappeared, leaving only the word "CROATOAN" carved on wood . Their fate remains one of the earliest American mysteries.

Some think they merged with local tribes, while others suggest they relocated. Without proof, the vanished colony remains a puzzle historians love to revisit.

5

The Taos Hum - New Mexico

Since the 1990s, some residents of Taos report hearing a low, steady humming sound . It’s described like a distant diesel engine idling in the desert.

Some studies suggest it may be related to low-frequency industrial noise or tinnitus in some individuals. The reality is, scientists have studied the phenomenon but haven’t pinned down a cause.

6

Marfa Lights - Texas

Out in West Texas, glowing orbs have appeared on the horizon for generations . They shimmer, split, and move in ways that seem inexplicable.

Tourists flock to Marfa hoping to catch a glimpse. Some suggest car headlights or atmospheric tricks, but the mystery remains.

7

Bloop-Like Ocean Sounds - Pacific Ocean

In the 1990s, NOAA hydrophones picked up a booming, low-frequency sound in the Pacific Ocean . Nicknamed "the Bloop," it was louder than known whale calls.

Theories ranged from icequakes to giant sea life. NOAA later concluded the sound was likely caused by large icequakes from Antarctic ice breaking apart.

8

The Upton Chamber - Massachusetts

Hidden in Massachusetts is a stone tunnel leading to a small underground chamber . Its age and purpose are still debated.

Some believe it was a colonial root cellar, while others argue it predates settlers entirely. Without records, the chamber remains an enigmatic piece of New England history.

9

America’s Stonehenge - New Hampshire

This site features stone walls, chambers, and standing slabs . Some argue it was built by Native Americans, while others see evidence of pre-Columbian visitors.

While some alternative theories suggest ancient origins, most archaeologists believe the structures are from the colonial-era. Whatever its origin, it’s a fascinating stop for curious travelers.

10

The Great Serpent Mound - Ohio

In southern Ohio lies a massive prehistoric earthwork shaped like a winding serpent . Stretching over 1,300 feet, it curves and coils across the landscape in striking detail.

Scholars agree it was built by Indigenous peoples, but its purpose is unclear. Some suggest it was a ceremonial site or calendar, while others see cosmic symbolism.

11

The Blythe Intaglios - California

Etched into the Colorado Desert, these giant figures depict humans and animals , some over 170 feet long. They’re best seen from the air, raising questions about how and why they were made.

Created centuries ago by Native Americans, their exact age and purpose remain uncertain.

12

Judaculla Rock - North Carolina

This large boulder is carved with hundreds of mysterious petroglyphs . Shapes, lines, and symbols cover its surface, their meanings long lost to time.

The Cherokee connect the markings to Judaculla, a legendary giant. Whether the rock was a sacred site, a map, or something else, the exact meanings of many carvings remain unknown.

1

Raven Rock Mountain Complex

Image: Ilagam

Did you know that in the 1950s, the US government carved out a secret underground city that could survive a nuclear attack? It’s called an "underground Pentagon", and very much like Area 51, it is one of the government's most classified projects.

This military complex and nuclear bunker is located near Blue Ridge Summit, Pennsylvania, 768 feet below the ground. It’s protected by 23.5 ft thick 30-ton doors built on top of springs to survive the shock from a blast. Raven Rock has five buildings with 15 floors big enough to live and work. The base has everything it needs to keep running, like a cafeteria, a barbershop, water generators, and even a medical center.

2

SubTropolis

Image: mwewering

Below Kansas City, Missouri, lies the world's largest underground business complex. SubTropolis is a structure located inside a mine north of the Missouri River. It was carved out of limestone some 135 to 185 feet underground and covers a total of 55 million square feet.

Kansas City Chiefs founder Lamar Hunt built this subterranean city in the 1960s. It has offices, storage space, and even factories. Over 1,600 people work here every day, largely because SubTropolis remains cool all year, making it an ideal location for businesses. Fun fact: some of Hollywood’s most beloved masterpieces are kept here, including the original film reels of Gone with the Wind and The Wizard of Oz.

3

Underground Atlanta

Image: Ronny Sison

Underground Atlanta is a historic spot in downtown Atlanta, Georgia. It was built in the late 1800s, right after the Civil War, as a commercial district centered around the railroad. In the 1920s, viaducts were built and the streets were raised, creating a second level of streets, buildings, and shops.

During Prohibition, the abandoned underground space served as the best spot for speakeasies and juke joints. For decades, people forgot about the hidden city, but in the 1960s, it was brought back to life as a fun place for music bars and nightlife.

4

New York City Subterranean World

Image: Photographer: unknown, Public domain, via Wikimedia Commons

Under America’s most populous city, there's a whole hidden world. For example, beneath Little Italy and the Public Library, there are secret vaults. Beyond the subway millions of people use daily, there is City Hall station, opened in 1904 and closed in 1945. It's a hidden gem with stained glass and mosaics that you can still visit by staying on the 6 train past the last stop.

But that’s not all! There are trading tunnels in SoHo and old cattle tunnels in the Meatpacking District. Also, in 1897, there were mail tubes built around the city to send letters between post offices that operated until the 1950s. Some of these underground spaces go as deep as 800 feet!

5

Permafrost Tunnel Research Facility

Image: Paxson Woelber

A large part of the land in the northern hemisphere is Permafrost, so it makes sense that there is a research facility specially built to study it. The Permafrost Tunnel in Alaska is the best place to learn about frozen soil that's over 40,000 years old.

The long tunnel was dug from 1963 to 1969 to study how to build and mine in frozen environments. Inside the facility, scientists study ice, ancient plants, and even bones from animals like mammoths. The tunnel shows different layers of earth, uncovering frozen ground from different time periods that help scientists anticipate what might happen as the world gets warmer.

6

The Greenbrier Bunker

Image: Alex Holzreiter

The Greenbrier Bunker in White Sulphur Springs, West Virginia, is a secret underground facility beneath a luxury hotel that has hosted numerous US presidents and famous guests. It was built during the Cold War to protect the US Congress in the event of a nuclear attack. The bunker was designed to house all 535 members of Congress and their staff for a long time.

This classified underground facility remained a secret until 1992, when a Washington Post article exposed it. Today, visitors can take tours to see special rooms, blast doors, and decontamination areas.

7

The Caverns

Image: jymy duhomme

Would you attend a concert underground? If you travel to Tennessee is totally possible! The Caverns, formerly known as Bluegrass Underground, is a very cool spot in Grundy County, Tennessee. Lying deep in a cave 333 feet underground, this concert venue with natural acoustics is the perfect place for live music.

People come from all over to hear a variety of performances, especially Bluegrass music. The Caverns can accommodate up to 1,200 people standing up and are equipped with state-of-the-art sound and lights. The cave's cool and quiet atmosphere makes the experience extra special!

8

Crystal City Underground

Image: Gustavo Alejandro Espinosa Reyes

Beneath the neighborhood of Crystal City, near Washington, DC, lies a network of shops, restaurants, and offices. It opened in 1976 and was designed to feel like an old shopping village with cobblestone streets and antique glass windows.

The underground space covers 150,000 square feet and connects several buildings. It's a popular spot for office workers and visitors, especially when the weather is bad. Unfortunately, in 2024, the shops closed, ending their retail era. Yet, the underground walkways and connections to the Metro remain open for pedestrians.

9

Los Angeles Prohibition Tunnels

Image: Alpha Perspective

In the 1920s, during Prohibition, people had to find ingenious ways around the restrictions on selling and consuming alcohol. That's why they built about 11 miles of underground tunnels right under Los Angeles.

Many of these subterranean sites are now closed, but you can still find a few hidden entrances around the city. You can even go on a tour to explore the tunnels and learn about their secret history.

10

Havre Beneath the Streets

Image: Đào Việt Hoàng

After a big fire in 1904 destroyed Havre’s business district in Montana, many shops moved underground. They used the old steam tunnels to stay safe from fires and bad weather. For years, the tunnels were busy with people and stores, such as saloons, drugstores, laundromats, and even a brothel. But today it is completely silent.

Fortunately, you can still visit what is left of this hidden city to see old shops and learn how people stayed safe and worked over 100 years ago. It's like going back in time!

11

Cheyenne Mountain Complex

Image: See page for author, Public domain, via Wikimedia Commons

One of the safest places in the world is right here in America, more specifically in El Paso County, Colorado. Hidden inside a mountain, Cheyenne Mountain Complex was built in the 1960s to protect the US military from nuclear attacks.

The bunker stands under 2,000 feet of solid Granite, making it super strong and safe. It was once the command center for NORAD (North American Aerospace Defense Command). The complex has blast doors that weigh 25 tons each and can withstand a nuclear blast. It also has its own power, water, and food supply. People could survive there for months!

12

Forestiere Underground Gardens

Image: Levi Clancy, CC0, via Wikimedia Commons

A Sicilian immigrant called Baldassare Forestiere spent 40 years digging and building a series of subterranean structures by hand in Fresno, California. Inspired by Roman catacombs and old wine cellars, he created around 65 rooms, tunnels, and courtyards to escape the hot summer sun.

The Gardens have fruit trees, grapevines, fishponds, and even a chapel. Some of the trees are more than 90 years old! Today, Forestiere Underground Gardens is a Historical Landmark you can visit if you want to discover a true underground paradise.

1

Boston, Massachusetts

The vast majority of Boston residents hold college degrees. With research-driven institutions like Harvard and Boston University, the city enables a rich academic environment that promotes learning, innovation, and scientific advancement in different fields. In addition, Boston's public schools and statewide educational standards rank among the best in the country!

2

Seattle, Washington

Seattle is definitely considered one of the smartest cities in the US! But why? Well, there are several factors. First, most of its population over age 25 (53.8%) holds a bachelor's degree or higher. And it's no surprise: Seattle is home to the University of Washington, one of the top-ranked universities in the world. In addition, the city is a tech hub, with one in five residents working in STEM fields (Science, Technology, Engineering, and Mathematics).

3

Chicago, Illinois

Chicago is a city everyone should experience at least once. Its rich cultural, intellectual, and innovative atmosphere secures its spot on this list. The city has a well-established education scene, with prestigious institutions like the University of Chicago and Northwestern University, and a high percentage of residents holding professional degrees in fields like law, medicine, and business. Plus, its smart use of technology to enhance life quality makes it stand out even more.

4

Atlanta, Georgia

Atlanta, Georgia, is succeeding in today's world thanks to its growing tech job market and fast internet speeds, making it an ideal place for anyone interested in science and technology. The city is also proud of its academic presence, with standout institutions like Emory University, Georgia Institute of Technology, and Georgia State University.

5

San Jose, California

If you're into technology, San Jose, California, might be your ideal city. As the heart of Silicon Valley, San Jose boasts an elevated number of highly educated residents: Over 26% hold a graduate or professional degree. It's also home to tech giants like Apple and Google, making it a hub of innovation and opportunity.

6

Durham-Chapel Hill, North Carolina

The metropolitan area composed of Durham and Chapel Hill in North Carolina is part of the renowned Research Triangle, named for the three major research universities in the region: Duke University, UNC Chapel Hill, and North Carolina State University. A significant portion of residents in this region hold graduate degrees, particularly in fields like medicine, science, and technology.

7

Boulder, Colorado

Sustainability, innovation, and education are top priorities in Boulder, Colorado. The city has been recognized for its commitment to the environment, including a bold goal of reaching 100% renewable energy by 2030. On top of that, Boulder was highlighted by Forbes as a major "intellectual center," ranking among the US cities with the highest percentage of residents holding a bachelor's degree or higher.

8

Austin, Texas

With over 19% of its residents holding a professional degree, Austin, Texas, has earned its spot on the list. In addition to the prestigious University of Texas fueling its educated population, Austin also has a rapidly growing tech industry. Its young, creative, and highly skilled workforce makes the city stand out even more.

9

Ann Arbor, Michigan

Thanks to its high concentration of highly educated residents, Ann Arbor, Michigan, regularly earns a spot on the list of the smartest cities in the United States. Much of that reputation comes from the University of Michigan, a major science, research, and tech hub, and the city's overall high level of educational attainment.

10

Washington, DC

Washington, DC, also ranks as one of the smartest cities in the country thanks to its high concentration of highly educated professionals, policy experts, and researchers. The capital city also boasts one of the highest graduation rates nationwide. From the Smithsonian Museums and the Library of Congress to the Kennedy Center and the National Archives, the city offers endless opportunities to enrich your cultural experience.