Mammoth Cave National Park

Geologists estimate that the oldest part of Mammoth Cave began forming around 10 million years ago. To date, explorers have surveyed and mapped more than 426 miles of cave passage, making Mammoth Cave by far the longest known cave system in the world, with explorers still discovering new passages. Over the course of several million years, underground rivers and streams carved out the underlying limestone creating a vast network of underground passageways.
We visited Mammoth Cave National Park in May 2025 while staying at the nearby Thousand Trails Diamond Caverns RV & Golf Resort near Park City, Kentucky. The Mammoth Cave Railroad Bike and Hike Trail ran alongside our RV park, and we were able to e-bike the 7 miles to Mammoth Cave National Park along this pleasant trail. The entire trail runs 9 miles between Mammoth Cave and Park City.

Mammoth Cave is so huge that the Park offers a total of 10 different cave tours, with at least one scheduled time daily for each tour. Reservations are required for the tours, and the NPS website advises that they often fill up a long way in advance. While most of the tours are guided by a Ranger, we chose to take the only self-guided tour known as the “Extended Discovery Tour”. This tour is available from 10 am to 2:30 pm each day and we were able to get same day walk-up reservations and immediate entry on the Sunday we visited. This tour took us a couple of hours including the hilly walk down to the entrance of the cave from the visitor center. This 1-mile tour covers a Y-shaped section of the cave with some very large passages.  The entry passage ended at a natural “Rotunda” with a historic salt peter mining site.
Saltpetre is a principal ingredient in black gunpowder, and mining saltpetre from the cave was extremely profitable in the early 1800’s and became even more so with the start of the War of 1812. Demand for gunpowder was at an all-time high during the war, as the importation of gunpowder had become very difficult due to the British blockade of many eastern sea ports. The War of 1812 ended in 1815, and the demand for saltpetre fell dramatically. Eventually the mining operation stopped, leaving behind mine workings that can still be seen at the Rotunda.

Huge open passages headed in both directions from the Rotunda. The scale of the cave passages was quite amazing, and the natural “flat roof” of the cave very impressive in its span. Rangers were stationed along the route and answered some of our questions about the cave’s history and its formation. We were struck by the lack of “cave decorations” (stalactites, stalagmites, etc.) in Mammoth Cave, which was quite a contrast from Carlsbad Caverns in New Mexico that we had visited a month earlier. While Mammoth Cave was formed by underground rivers, it is now largely a “dry cave” with its sandstone cave roof preventing water penetration into the cave. Without any water penetration there is no mechanism for the formation of cave decorations which rely on eons of mineral-rich water dripping into the cave through the roof.

We enjoyed our half day visit and were impressed by the spectacular scale of the caves. The self-guided tour we took seemed like a good introduction to the cave system. A multiday visit to the park would be required to take some of the many Ranger-led cave tours that are available.

Photos from our visit to Mammoth Cave National Park are included at the end of this post.