1

Seattle Underground City

Did you know the remnants of Seattle's original streets are still accessible? Beneath the bustling streets of modern-day Seattle lies the Underground City , a network of subterranean passageways that formed the ground level in the 1800s.

By the end of the 19th century, after the Great Seattle Fire, it was decided to rebuild the city at a higher elevation to combat frequent flooding . So, these original streets, sidewalks, and storefronts were buried, and with it, much of their history.

Guided tours take people through tunnels and ladders and retell real and eerie stories about the history of the Underground City.

2

Luray Caverns

Image: Robert Thiemann

Have you ever heard of the underground Stalacpipe Organ ? Not only is it a one-of-a-kind interaction between keyboards and cavern stalactites, but it is also the largest musical instrument in the world, according to Guinness World Records.

This instrument lives in the Luray Caverns, Virginia. It consists of an electric console that taps on these ancient stalactites of varying sizes to produce musical tones. A subterranean wonder, these caverns are also known for their extraordinary size , housing towering stalactites and stalagmites, mirrored pools, and delicate drapery-like calcite formations.

3

The Underground Gardens of Baldassare Forestiere

Image: Adrian Botica

This stunning subterranean retreat was built entirely by hand. Tucked under the sun-scorched landscape of Fresno, California, lie the Underground Gardens of Baldassare Forestiere . They are the life’s work of Baldassare Forestiere, a Sicilian immigrant who started digging in the early 1900s to escape the Central Valley's oppressive heat.

Over 40 years, drawing inspiration from ancient Roman catacombs , Forestiere carved an elaborate network of underground rooms, passageways, grottoes, and courtyards that span 10 acres.

A unique masterpiece, the gardens are open with guided tours that lead guests through beautifully designed spaces featuring skylights, arches, and alcoves. This oasis also boasts an array of fruit trees, including citrus, figs, and olives.

4

Ruby Falls

Image: Goodfreephotos_com

Colorful and breathtaking, the Ruby Falls is a geological wonder located inside Lookout Mountain near Chattanooga, Tennessee.

Hidden over 1,000 feet below the mountain's surface, this waterfall cascades 145 feet into a pool , making it one of the tallest underground waterfalls open to the public.

Visitors enter the mountain and descend via elevator. Then, they walk through stunning cave formations such as stalactites, stalagmites, and flowstone. At the waterfall chamber, multicolored lights –powered by renewable energy– illuminate the falls. Lantern-lit tours are also offered as a chance to visit the marvel with a different charm.

5

The Catacombs of Green-Wood Cemetery

Image: Joy Ernst

Arched tunnels of tranquil, sacred vaults lie beneath the Green-Wood Cemetery in Brooklyn, New York. Built in the mid-19th century, these catacombs were designed as a prestigious resting place for the city’s elite , prominent families.

While the catacombs are typically closed to the public, special events are sometimes organized to welcome visitors, such as art expositions, guided history tours, and candlelit tours seasoned with live music and storytelling.

Outside, where the sun does reach, await the serene landscapes and remarkable monuments of the cemetery, which is itself a National Historic Landmark .

6

The Lost Sea

Image: Roberto Nickson

The largest underground lake in America is in Tennessee. Hidden within the Craighead Caverns in Sweetwater, this enormous body of water lies in a cave system filled with fascinating formations, such as stalactites, stalagmites, and rare anthodites, also known as "cave flowers."

A National Natural Landmark, this lake marvels scientists, who are yet unaware of the exact extension of its waters. Those who visit can embark on a boat ride called "The Lost Sea Adventure," first walking inside the cavern before reaching a boat to navigate these ethereal sights.

7

Mammoth Cave National Park

Image: Sherin Jacob

The Mammoth Cave National Park is home to the longest cave system in the world . Located in central Kentucky, it extends over 420 miles of explored passages and many more likely undiscovered. Enormous chambers, underground rivers, a labyrinth of tunnels, and gypsum crystal formations can all be found at this site.

The park has been declared a UNESCO World Heritage Site and an International Biosphere Reserve. It also includes over 52,000 acres of protected land on the surface, renowned for its lush forests and diverse wildlife.

8

Carlsbad Caverns National Park

Image: Cason Asher

A large bat colony lives in the Carlsbad Caverns National Park in New Mexico, but that’s not its only charm. The park boasts over 100 caves, with its centerpiece being the immense Carlsbad Cavern.

The cavern includes the Big Room, one of the largest underground chambers in North America, spanning 8.2 acres. Visitors can descend via an emblematic natural entrance or by elevator, dropping 750 feet underground. Stalactite formations like the Giant Dome, the Hall of the White Giant, and the Chandelier are some of the caves' breathtaking highlights.

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Indian Echo Caverns

Image: Magda Ehlers

The Indian Echo Caverns, which have been open to the public since the early 1920s, are carved into the limestone of the Appalachian Mountains. Located near Hummelstown, Pennsylvania, this site gets its name from the echoes heard within the cavern’s chambers , which were once believed to be mystical by Native American people in the area.

Unique, immersive sections of the caverns have names like the "Crystal Palace," the "Echo Room," and the "Wedding Room," where, yes, real weddings are sometimes held!

10

Wind Cave National Park

Image: Francesco Ungaro

Wind Cave National Park, located in the Black Hills of South Dakota, is one of the world’s largest caves, but that’s not what it’s most famous for. One signature sight here is the boxwork formation , a rare lattice-like pattern formed by calcite deposits.

The cave system stretches for over 140 miles, though much of it remains unexplored. Popular tours take guests through captivating features like the "Ribbon Room" and the "Crystal Palace."

Why is Wind Cave called that? Mainly due to the "wind" phenomenon that occurs at its entrance. The cave's air pressure causes the entrance to draw in or expel air, depending on atmospheric conditions.

1

Lewis and Clark (1804–1806)

Image: Museum of New Zealand Te Papa Tongarewa

Everybody knows about Lewis and Clark and their glorious quest across the nation, but what most don’t know is that they originally set out to find a continuous water route, the fabled Northwest Passage, from the Mississippi River to the Pacific Ocean. Commissioned by President Jefferson, the journey was meant to open up western trade routes.

Although they reached the Pacific, they confirmed that no such navigable waterway existed. Their journey was a landmark of exploration, but their primary goal remained unaccomplished .

2

Lady Franklin Bay Expedition (1881–1884)

Image: David BP

The 1881 Adolphus Greely-led expedition aimed to establish a scientific research station in the high Arctic and gather meteorological and astronomical data as part of the First International Polar Year.

But two relief ships failed to reach them due to ice. Stranded for over two years, only 7 of 25 men survived. While some data was collected, the mission was a logistical and human failure .

3

Frederick A. Cook (1908)

Image: Roxanne Desgagnés

American explorer Frederick Cook claimed he reached the North Pole in 1908, beating Robert Peary by a year. His announcement stirred immediate controversy and public excitement.

However, Cook failed to provide verifiable proof, and his claim was largely discredited . He also falsely claimed the first ascent of Denali. His goals, while grand, were never validated .

4

Amelia Earhart (1937)

Image: Shaun Bell

Amelia Earhart sought to be the first woman to fly around the world along the equator. Her journey was a bold attempt to push the limits of aviation and global navigation.

Tragically, she vanished over the Pacific near Howland Island. Despite massive search efforts, neither she nor her plane was found. Her historic goal remains unfulfilled .

5

USS Jeannette Expedition (1879–1881)

Image: Hector John Periquin

The Jeannette Expedition set out to reach the North Pole via the Bering Strait, based on a theory that a warm current could carry ships through the ice.

Instead, the ship was trapped and crushed by ice. The crew made a desperate trek across Siberia, with many dying from exposure and starvation. The pole was never reached , and the voyage ended in tragedy.

6

Crocker Land Expedition (1913–1917)

Image: Annie Spratt

Backed by Robert Peary’s reports, this expedition aimed to locate "Crocker Land," a supposed Arctic landmass seen on a prior voyage.

After weeks of travel, they discovered it was a mirage. The team was stranded for years due to failed rescue attempts. Their quest failed because the land never existed .

7

American Karakoram Expedition (1953)

Image: Daniel Born

Led by Charles Houston, the expedition aimed to be the first to summit K2, the world’s second-highest mountain after Everest. The team climbed high and established advanced camps.

Trapped by a severe storm, they made a heroic retreat. One climber died, and the summit remained out of reach . Their attempt was noble, but ultimately unsuccessful.

8

Ziegler Polar Expedition (1903–1905)

Image: ArcticDesire.com Polarreisen

The abundance of Arctic expeditions on this list is not a coincidence. This area is tough to traverse, and much of it remains unknown. This particular expedition sought to reach the North Pole via Franz Josef Land. The crew wintered in the Arctic with supplies and dogs for the attempt.

Severe ice and harsh conditions thwarted their progress. They were stranded for two years and never neared the pole. Though most survived, the mission failed in its main goal .

9

Zebulon Pike (1805)

Image: Mathew Benoit

In 1805, Army officer Zebulon Pike was tasked with exploring the headwaters of the Mississippi River. The goal was to identify its true source and assert U.S. presence in the newly acquired Louisiana Territory.

Facing poor maps, freezing conditions, and supply shortages, Pike never reached the actual source . Though he gathered useful data, the mission failed to meet its primary objective.

10

American China-Everest ’82 Expedition (1982)

Image: Andreas Gäbler

Led by Lou Whittaker, this team aimed to summit Mount Everest via the remote Chinese (Tibetan) side, which was an unusual and challenging route for American climbers at the time.

Despite significant progress, they turned back just 1,500 feet from the top due to difficult conditions. The summit remained unreached .

1

Mississippi River

Image: Justin Wilkens

Beloved by blues musicians and immortalized by Mark Twain, the Mississippi has been central to exploration, trade, and American identity. The name comes from the Ojibwe/Anishinaabe word misi‑ziibi, meaning "Great River" or "Father of Waters."

Flowing some 2,320 miles, its watershed drains roughly 41% of the continental U.S., and its vast system remains critical for both commerce and agriculture.

2

Missouri River

Image: Jayden Herr

The name of the Missouri River comes from the Algonquian term ouemessourita, meaning "people with dugout canoes."

A crucial highway for early explorers like Lewis and Clark, as well as later settlers, this 2,300-mile-long river was once home to Native tribes such as the Missouria. Today, it remains a vital part of regional agriculture and river transport.

3

Hudson River

Image: Harry Gillen

Originally called Muh-he-kun-ne-tuk ("waters that are never still") by the Mohicans, the river was later renamed after Henry Hudson, who explored it in 1609 for the Dutch East India Company.

The Hudson Valley later grew into both an economic and cultural hub, inspiring the Hudson River School of painters and playing a strategic role during the American Revolution.

4

Colorado River

Image: Mike Newbry

The name Colorado comes from Spanish, meaning "reddish," a reference to the red silt once carried by the river. Before 1921, its upper course was known as the Grand River, until Congress renamed it to reflect the state of Colorado.

Over millions of years, the Colorado River carved the Grand Canyon, one of the world’s most dramatic natural landscapes. Today, it supports irrigation across seven U.S. states and northern Mexico and generates hydroelectric power through major dams such as Hoover Dam and Glen Canyon Dam.

5

Rio Grande

Image: Sara Cottle

The name Rio Grande means "Big River" in Spanish. Serving as the border between the U.S. (Texas) and Mexico, it has defined geopolitical boundaries since the end of the Mexican-American War in 1848.

Historically, the Rio Grande supported Indigenous communities such as the Pueblo and Apache peoples, and later Spanish missions and settlements. Today, it serves as a lifeline for agriculture, cities, and wildlife habitats across the arid regions of Texas, New Mexico, and northern Mexico along its 1,896-mile course.

6

Ohio River

Image: Joshua Canter

"Ohio" comes from the Seneca word ohi:yo’ , meaning "good river" or "large creek." Formed by the confluence of the Allegheny and Monongahela Rivers at Pittsburgh, it flows for about 981 miles through six states before joining the Mississippi River.

In early America, the Ohio was a key route for westward expansion and trade. Settlements along its banks grew into important commercial and industrial centers, including cities like Cincinnati, Louisville, and Pittsburgh, and its fertile floodplains supported agriculture that fueled the growing nation.

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Columbia River

Image: Stephen Walker

The Columbia River was named after the Columbia Rediviva , the ship captained by Robert Gray , which itself was named in honor of Christopher Columbus. For thousands of years, the river served as a vital trade network for numerous Native American tribes, and later became central to the North American fur trade.

Its fertile valleys supported settlements and agricultural development throughout the Pacific Northwest. Today, the Columbia is a major source of hydroelectric power, with major dams such as Grand Coulee and Bonneville supplying electricity to millions of people.

8

Potomac River

Image: Sara Cottle

The name "Potomac" comes from a Native Algonquian word, likely Patawomeck (probably Piscataway), meaning "river of swans." The river flows past Washington, D.C., and George Washington’s Mount Vernon estate overlooks it.

During the colonial era and the Civil War, it was a crucial transport route, and its watershed continues to hold historical, cultural, and political significance today.

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Delaware River

Image: Clay Banks

Named after Lord De La Warr (Thomas West), an English nobleman and colonial governor, the Delaware River is best known for George Washington’s daring 1776 crossing, which surprised Hessian troops in Trenton and provided a crucial morale boost for the Continental Army during the Revolutionary War.

Over the years, the river has remained vital for trade and industry, shaping the mid-Atlantic economy and supporting major ports in New Jersey, Pennsylvania, and Delaware.

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Susquehanna River

Image: Jennifer Wick

The name "Susquehanna" likely comes from the Lenape word siskëwahane, meaning "Muddy River" (though other translations, such as "Oyster River," have been proposed). One of the oldest river systems in North America, the Susquehanna stretches about 444 miles from New York through Pennsylvania to the Chesapeake Bay in Maryland.

It supported Indigenous communities such as the Susquehannock, and early colonial settlements relied on it for transport, fishing, and trade. Its fertile valley later powered mills, contributed to the region’s coal and lumber industries, and played a key role in shaping the development of the Mid-Atlantic.