What better time to learn about and plan a visit to a cave than this year, dubbed the first ever  International Year of Caves and Karst by the International Union of Speleology. Karst can be found worldwide where water has gradually worn away rock, usually limestone, over millions of years. This erosion forms caves and related structures like natural bridges, sinkholes, and sinking streams. Karst caves contain spectacular speleothems (cave formations) like stalactites, stalagmites, flowstones, columns, curtains, and boxwork.

Beyond the awe factor, caves are important ecologically, culturally, and historically. According to the National Park Service, up to 40% of ground drinking water in the U.S. is from karst aquifers. They harbor rare, endemic, and endangered species which rely on the specialized cave environment.

Caves provide a window into our collective past. Their history is measured in millions of years. By studying them, we can better understand how the earth was formed and changed through millennia. Artifacts like pictographs, tools, and Mayan objects were preserved in cave environments and give us insights into how our forebearers lived in this place.

The following seven state parks feature caves open to visitors. Check individual park websites for restrictions and reservation requirements. Be a good guest by not touching cave formations. And follow precautions for White Nose Syndrome, a fungus that has decimated bat colonies across the U.S.

Carter Caves State Resort Park, Kentucky

Carter County has the highest concentration of caves in Kentucky – over 290 – and Carter Caves State Park contains nearly 40 of them. According to naturalist Paul Tierney, the area has the perfect recipe for karst geology: 320-million-year-old Mississippian limestone, plentiful water, and carbonic acid from the forest that erodes the rock. Along with the caves, hikes in the park lead to above-ground karst formations including several natural bridges and a box canyon.

Several caves here are closed seasonally because of the hibernating populations of federally endangered Indiana Bats. Their clusters contain up to 20,000 bats in one room and they eat a massive number of insects. Saltpetre Cave served as a mine during the War of 1812. Manufacturing black gunpowder required potassium nitrate, or saltpetre.

The Park offers a varied selection of cave tours including the developed Cascade Cave with cave formations, colorful limestone, and a 30-foot underground waterfall. Bat Cave and Saltpetre Cave both have more adventurous walking and crawling tours. Two additional cave systems are open to self-exploration with a permit.

Maquoketa Caves State Park, Iowa

This unusual state park is the choice for DIYers. A 6-mile trail threads throughout the park, leading hikers to scenic overlooks and the 13 caves open for self-guided exploration. Some are easy to walk in for all ages and some are for adventurous spelunkers who don’t mind getting wet and muddy. Visitors can pick up a brochure to orient themselves and interpretive panels on the trails explain the geology and history of the area.

One of the most accessible is Dancehall Cave. As its name suggests, it housed a stage and hosted community dances in the horse and buggy era. The Park also hosts bats, including tri-color and little browns, during their winter hibernation.

Visitors need to bring their own equipment: flashlights, helmets, knee pads, and old clothes. Maquoketa can be popular on summer weekends, especially from 11am – 4pm, and they turn people away once their parking lots are full.

Kartchner Caverns State Park, Arizona

Kartchner Caverns might be the most pristine cave accessible to the public in the United States thanks to determined conservation efforts. It had a grapefruit-sized original entrance and no indication of historical human use when discovered in the 1970’s. Until its opening as a state park in 1999, only a handful of people had been inside. In fact, the footprints of the original explorers are still visible off the public access trail.

Kartchner Caverns (Photo: Arizona State Parks and Trails)

This level of care has preserved a lavish, colorful, and dynamic living cave environment, with soda straws, curtains, stalactites, and stalagmites, and a 58-foot-tall column named Kubla Khan. The two cave rooms have been visited by other animals, and the visitor center displays fossils and bat skeletons found inside. At least one species of macroinvertebrate was a new species to science.

The Park leads ADA accessible guided tours of the caves. Reservations are recommended. For further preservation, taking photos is not allowed in order to maintain optimum temperature for the fragile formations.

Longhorn Cavern State Park, Texas

The walls of Longhorn Cavern look more like a slot canyon than a typical karst cave. An ancient underground river eroded and sculpted a smooth channel through the limestone and the undulating walls are accented with large deposits of gleaming calcite crystals. It features one of the largest known dolomite chambers in Texas, the Hall of Marble.

Longhorn Hall of Diamonds (Photo: Longhorn Cavern State Park)

The cave is also an excellent place to view tri-colored bats. One of the smallest bats in North America, they can be spied from the pathway most of the year.

In the 1930’s, the Civilian Conservation Corps made the entire cavern accessible to state park visitors. Over 6 years, they removed 3,000 dump trucks worth of river debris – by hand. In 1967, the cavern was licensed and stocked as a Cold War fallout shelter for almost 2,000 Texans in the event of nuclear war.

Visitors can choose between the walking tour on a developed path and a Wild Cave Tour through some of the cave’s lower tunnels. Safety gear is included with the Wild Cave Tour.

Onondaga Cave State Park, Missouri

Missouri is home to more than 5,500 caves, earning it the moniker of the Cave State. The karst geography is due to the shallow seas that covered the Ozarks millions of years ago. Their sediment formed the limestone that covers much of the region now. Signs of the ancient sea can be viewed in Cathedral Cave. Cave formations called stromatolites, fossilized mounds of photosynthetic algae, rest in an ancient exposed reef. The trail in Onondaga Cave follows an underground stream with rimstone dams surrounded by stalactites, stalagmites, flowstones, and cave coral.

Inside Cathedral Cave is a Seismic Station, an underground earthquake monitoring node. Data is sent to the National Earthquake Center in Golden, Colorado. A spring from Onondaga Cave powered a gristmill for grinding corn and wheat into meal and flour, and a remnant of the foundation is in the park.

Guided tours are available for both Onondaga and Cathedral. Cathedral Cave is a wilder experience with lantern lighting and requiring a short hike to the cave entrance.

Pictograph Cave State Park, Montana

These marine sandstone alcoves in the base of towering 200-foot cliffs have sheltered people for thousands of years. For prehistoric people, they provided warmth and proximity to medicinal plants like mint and yuccas. An archeological dig in the 1930’s uncovered more than 10,000 artifacts in the cave floors. Some of these arrow heads, baskets, and paintbrushes are on display at the park visitor center.

Pictograph and Ghost Caves. (Photo: Montana State Parks/Montana FWP)

The rock shelters harbor over 100 pictographs, some of which are over 2,000 years old. However, most guests only see 1/10th of them because of the unique geology of the park. Most are veiled due to a thin layer of natural mineral deposits. These are revealed in rain as water flows over the minerals on the cave ceiling and makes them translucent. This unique ghost writing effect makes the park a sacred place for both historic and modern peoples like the Crow.  

Visitors can hike a 3/4-mile loop trail to the interpretative displays at both Pictograph and Ghost Caves. While binoculars are helpful for seeing the rock art, park staff recommend the DStretch app that enhances the colors and outlines of the drawings.

Providence Mountains State Recreation Area, California

Originally developed as a Route 66 roadside attraction, Mitchell Caverns is now in a state recreation area in the midst of the remote Mojave National Preserve, one of the newest national parks. But with two large entrances situated 1,000 feet above the valley floor, referred to as the sacred eyes of the mountain, the caverns have always been a prominent feature of the area.

Mitchell Caverns (Photo credit: copyright California State Parks, all rights reserved)

Perhaps the first visitor was a giant Shasta Ground Sloth. An arm bone found in the cave dates to over 10,000 years old. Evidence shows early peoples stored some of the abundant pinyon pine nuts in the caves’ shelter. Modern visitors come for the cave formations, like a rare shield perpendicular to the floor and two feet up the wall.

Mitchell Caverns still has the feel of a nostalgic roadside attraction. Tours are kept to a small number and are only reservable by phone. They book up months in advance. Road conditions are primitive and the nearest town is 60 miles away, so visitors should bring ample fuel, food, and water for their stay.