Places the Highway Heads guides send you below ground: lava tubes, show caves, a working salt mine, a buried city street and a drinking-water reservoir turned echo chamber.
16 stops across 12 states, taken from the Highway Heads city guides.
Arizona
Lava River Cave
A free, mile-long lava tube about 14 miles from town that holds near-40°F temperatures year-round no matter the season outside, formed roughly 650,000–700,000 years ago and discovered by lumbermen in 1915. There is zero ambient light once you’re inside — bring at least two flashlights per person.
Kansas
Strataca
The underground salt museum in part of the worked mine, formerly the Kansas Underground Salt Museum. The museum's site lists tour hours of 9 a.m. to 3 p.m. Tuesday to Saturday and 1 p.m. to 3 p.m. Sunday, closed Monday, says tour times and schedules may vary based on events, and says reservations are recommended because walk-ins are not guaranteed. The Salt Blast Pass, the main tour, is listed at $35 for adults ages 13 and up and $23 for seniors (60+) and military; other rates are on the ticket page, and visitors must be 4 years of age or older to tour the underground museum. The site lists general underground admission and the dark ride as handicap accessible, and the train ride, salt safari and lantern tour as not.
Kentucky
Lost River Cave
A cave with its own underground river, once home to an air-conditioned 1930s-60s nightclub billed as the only one of its kind in the country; today it's a 45-minute boat-and-walking tour through the same passages.
Mammoth Cave National Park
The longest known cave system on Earth, with more than 426 surveyed miles of passageway — over one and a half times longer than the runner-up. Tours range from an easy one-hour walk to muddy, crawling “wild” routes.
Missouri
Montana
Lewis and Clark Caverns State Park
Montana’s first state park (1938), with two guided tours through limestone caverns formed over 300 million years ago; the explorers it’s named for never actually went inside.
New Mexico
The bat flight at the caverns
From spring through October the park runs a free ranger talk at the Bat Flight Amphitheater by the natural entrance, before the colony leaves for the night; the Park Service says the strongest flights are usually August and September, seating is first-come, and no cameras or electronic devices are allowed. Its own pages give the season as April to October in one place and late May to October in another, so check the current listing. The park runs a programme around it; confirm the season and timing, which depend on the colony rather than the calendar.
New York
Howe Caverns
A limestone cave discovered in 1842 when a farmer noticed his cattle gathering near a hillside opening; the show-cave route runs nearly a mile and a half at a constant 52°F.
Texas
The Cistern, Buffalo Bayou Park
An 87,500-square-foot former underground drinking-water reservoir for the city, decommissioned in 2007 and reopened as a strange, echoing art space you tour by walkway over a shallow reflecting pool.
Natural Bridge Caverns
Four college students found these caves in 1960 on their fourth trip underground; they opened to the public in 1964 and remain the largest commercial caverns in Texas, with tours descending 180 feet into a constant 70 degrees.
Utah
Timpanogos Cave National Monument
In American Fork Canyon, which the National Park Service places approximately 40 miles south of Salt Lake City, reached by a steep mile-and-a-half hike to the cave entrance. Tours are ticketed, with tickets sold through Recreation.gov up to 30 days ahead, and the park describes the tour season as typically running from May or June through September or October.
Virginia
The Great Stalacpipe Organ, Luray Caverns
Guinness’s largest musical instrument on Earth, spread across 3.5 acres of cave and played by solenoid-fired mallets tapping stalactites tuned by hand over three years.
Skyline Caverns, Front Royal
Home to rare anthodite crystals — formations that spread outward in all directions instead of hanging down, found in only a few caves in the world; the cavern says its 18-inch Chandelier is the largest and oldest anthodite known.
Washington
Seattle Underground Tour
A 75-minute walk through the storefronts and sidewalks Seattle buried under its own raised streets after the 1889 fire, starting from below Doc Maynard’s Public House at 614 1st Avenue.
Wisconsin
Cave of the Mounds
A limestone cave system under a Wisconsin farm, discovered by dynamite in 1939 and open ever since. About 40 minutes west of downtown.
