Great Onyx Cave Lantern Tour at Mammoth Cave National Park

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For reviews of all Mammoth Cave National Park tours, how to get tickets, what to wear, and rules for the tours, see the Cave Tours web page here on National Park Planner. Keep in mind that not all tours are offered year-round, and the schedule of what tours are available changes often. Be sure to check the National Park Service’s official Cave Tours web page for the current schedule.

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OVERVIEW

All visitors to Mammoth Cave National Park should take one lantern tour to see a cave just as all early tourists did—by lantern light. Three are offered—Great Onyx Lantern Tour, Star Chamber Lantern Tour, Violet City Lantern Tour—and all have their benefits. But if I had to pick one, it would be the Great Onyx tour, and for three reasons.

First, the Great Onyx Cave, while within the boundary of Mammoth Cave National Park, is not connected to Mammoth Cave. It is a separate cave that was discovered in 1915 and actually competed with Mammoth Cave for tourists, even after the park was created in 1941. It remained in private hands until the National Park Service acquired it in 1961. Because it is a separate cave, the Great Onyx Lantern Tour does not overlap with the routes of any other cave tours. Many tours of Mammoth Cave itself do have overlapping routes, some to the extent that they are complete duplicates of each other. By choosing the Great Onyx Lantern Tour, you do not have to worry about seeing the same things twice when making a tour schedule for your vacation.

Lanterns illuminate the Great Onyx Cave in Mammoth Cave National Park

Second, if you have been inside Mammoth Cave, you most likely noticed that the large majority of the passageways lack speleothems, which is the collective name for stalactites, stalagmites, and other calcite formations most people associate with a cave. This is because speleothems require slow, dripping water to form, and a sandstone caprock covers most of Mammoth Cave, preventing water from entering. The sandstone cap is patchy in the area surrounding the Great Onyx Cave, so water does get in, and it has created passageways that are full of calcite formations that tourists want to see.

Speleothems inside the Great Onyx Cave in Mammoth Cave National Park

Stalactites and stalagmites inside the Great Onyx Cave, Mammoth Cave National Park

Third, as far as cave tours at Mammoth Cave National Park go, the Great Onyx Lantern Tour is one of the easier ones. There are only 82 stair steps compared to hundreds on some of the other tours, and only one mile of walking is required. Furthermore, you don’t have to walk up and down the steep hill from the Mammoth Cave Visitor Center to the Historic Entrance of Mammoth Cave, which is something I dread more than any staircases inside. The Star Chamber Lantern Tour is also one of the easier tours, but Violet City—my second choice of lantern tours—is extremely difficult; participants need to be in good physical shape. Those seeking an easier option should choose either the Star Chamber or the Great Onyx tour.

Staircase inside the Great Onyx Cave in Mammoth Cave National Park

The Great Onyx Lantern Tour is a little over two hours long. Participants must be at least six years old to attend, and anyone under the age of 16 must be accompanied by someone 18 or older. A bus takes tour participants to the cave. All tours requiring a ride depart from Shelter B just outside the Visitor Center.

Shelter B meeting area for cave tours at Mammoth Cave National Park

Only tour participants 16 and older can carry a lantern. There aren’t enough lanterns for everyone, so you don’t have to be bothered with carrying one if you don’t want to. The typical arrangement is one or two per family group. Because Great Onyx Cave does not have a high ceiling in most places, the lanterns actually provide plenty of light to see the tour path and the cave formations even if you are not holding one or standing next to somebody who is.

Ranger conducts the Great Onyx Lantern Tour at Mammoth Cave National Park

INSIDE THE CAVE

The Great Onyx Lantern Tour begins by heading down a flight of stone stairs created long before safety was a concern for tour operators. As the Ranger giving my tour said, “The steps are not OSHA compliant.” There is, however, a modern railing attached to the cave wall.

Stairs just inside the entrance to the Great Onyx Cave in Mammoth Cave National Park

The first part of the Great Onyx Cave is quite tight, with low ceilings and narrow passageways. There are many stalactites, stalagmites, columns (stalactite and stalagmite that grew together), and flowstone, which are formations that drip down the walls. Many formations are still growing, which means water is still getting into the cave. The tiny stalactites on the ceiling may already be 100 to 300 years old, and the larger formations hundreds of thousands of years old.

Speleothems near the entrance of the Great Onyx Cave in Mammoth Cave National Park

Stalactites, stalagmites, columns, and flowstone inside the Great Onyx Cave in Mammoth Cave National Park

When Great Onyx Cave was privately owned, there was a fee to see just the entrance area and an additional fee to explore farther. Because the entrance was so spectacular, most people paid for the longer tour. But as you proceed farther into the cave, notice that it actually gets larger and is not much different from Mammoth Cave. Wherever you see barren walls and ceilings, this is an area covered by the sandstone caprock. But don’t worry, because you and the visitors of the past aren’t going to get ripped off because the caprock is patchy, so the speleothems do reappear deeper into the cave.

Great Onyx Lantern Tour proceeds farther into the cave, Mammoth Cave National Park

Large and dry open areas of the Great Onyx Cave are sections located under the sandstone caprock, Mammoth Cave National Park

While the ceilings in these dry areas appear barren, shine a light on them and you might see sparkles. This is gypsum, and it only grows in dry caves when moisture in the rocks evaporates, creating calcium sulfate dihydrate crystals (gypsum). Depending on the crack or openings in the rocks, the crystals form different shapes, some flower-like, some as large a celery stalks or deer antlers.

Ranger leading the Great Onyx Lantern Tour at Mammoth Cave National Park shines a light on the gypsum crystals growing on the ceiling

Gypsum crystals growing on the ceiling of the Great Onyx Cave in Mammoth Cave National Park

The tour ends about a half mile into the cave, at which point the group turns around and proceeds back to the entrance. The Great Onyx Cave is about seven miles long, but getting to most of it requires crawling. The lantern tour covers roughly two-thirds of the walkable passageways.

Exiting the Great Onyx Cave at the conclusion of the Great Onyx Lantern Tour, Mammoth Cave National Park

Great Onyx Lantern Tour participants board the bus back to the Mammoth Cave Visitor Center

There are only three other tours at Mammoth Cave National Park where visitors can see a large collection of speleothems: the Wondering Woods Tour, which also visits a cave not connected to Mammoth Cave, and the Domes and Dripstones and Frozen Niagara tours within Mammoth Cave, though both visit the same area of calcite formations, the Frozen Niagara. Domes and Dripstones is a longer and much more difficult tour that explores other passageways, whereas the Frozen Niagara Tour heads directly to the Frozen Niagara and exits after seeing it. It is one of the easiest tours in the park. No need to take both, and I recommend Domes and Dripstones if extra physical activity does not bother you.

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