What do you do in Bowling Green? You visit the National Corvette Museum. Bowling Green is home to both the Corvette Museum and the Corvette factory.

Fun fact: on February 12, 2014, a sinkhole opened beneath the museum and swallowed eight Corvettes.

This part of Kentucky sits above miles of cavern, as we discovered when we visited Mammoth Cave. Mammoth Cave is the longest known cave system in the world; more than 400 miles of cave passages have been surveyed, with countless additional miles yet to be explored. The bit under the Corvette Museum aside, most of the limestone cave system lies under a sandstone layer which protects the cave ceilings from water erosion and eventual collapse.

The first section we visited had been a saltpeter mine (worked by slaves, naturally) during the War of 1812. After the war, the demand for black gunpowder shrank, so the cave owners—the caves were owned privately until the government bought the land, in 1926—opened the caves to tourists. These visitors (and soldiers who used the caves during the Civil War) used candle smoke to write their names on the cavern ceiling. Anyone caught doing that today would be charged with a felony.

In other parts of the cave, water did come in through sinkholes, which resulted in the more familiar sorts of rock formations.

We also visited Bernheim Forest, to see the Forest Giants. These giants—named Mama Loumari, Elina, and little Nis—are the works of Danish artist Thomas Dambo, who built them from recycled wood.

Next: bits of Tennessee and North Carolina