In the 19th century, Kentucky's Mammoth Cave launched an entire, very competitive cave tourism industry in the area, In 1925, Floyd Collins was trapped in the cave system, which was the beginning of the end of the cave wars.
Research:

Behind the Scenes Minis: Stairs and Trains
29:25

Elizabeth Blackwell's Curious Herbal
34:51

The Many Meanings of the Bunker Hill Monument
45:48