Mammoth Caves National Park, in central Kentucky is the longest known cave system in the world with over 348 miles (557 km) explored and mapped.

While the park is primarily designed to protect the cave system, there are also more than 70 miles (112 km) of hiking and horseback trails through the wooded hills above ground. Trails to several springs in particular, and those along the Green River are well worth the hike. Due to poor weather conditions (heavy rain) during our visit, we didn't spend too much time on the trails. This is one of the many small cave entrances one might come across while hiking. (Note: these are not open to the general public outside of arranged tours).

Mammoth Caves runs a huge variety of tours through the caves ranging from one hour to all day. The park is strewn with entrances into the cave. These include the "historic entrance" near the visitor center, as well as small buildings containing nothing but a stairwell into the ground, and doors leading directly into hillsides. Despite the large number of tours offered, many of them do not overlap at all. The exact routes tend to change over time as well.

This feature is known as the "Frozen Niagara" and is the focal point of the tour of the same name. Large expanses of the caves are sheltered under bedrock which does not allow water to seep through. As a result, there are no stalactites or stalagmites in those sections. Other areas lie beneath limestone and produce columns like this one.

Historically, some tours included an underground boat ride on the ominously named River Styx. Due to the deterioration of old wooden structures built to facilitate those tours, visitors can no longer cross the river. As a result it's unusual to see any of the few true cave-dwelling species that live in Mammoth Caves such as eyeless cave shrimp and eyeless fish.

Most of Mammoth Caves tours are aimed at largish tour groups. There are frequent breaks in large caves for explanations, and while a lot of stair-climbing is generally required, most tours aren't particularly strenuous. They do offer a more interesting spelunking-style trip. In the winter months these are uncommon so we were unable to take one. We hope to return in the future for one of those more challenging tours.