|Great Saltpetre Cave (RK-5) meets National Register Criterion A, of importance for two uses, each spanning two different Periods of Significance. The Cave served 1798-1815 as an important site of extraction of saltpeter, a necessary ingredient of gunpowder. At the turn of the 19th century, purchasing gunpowder from England was less expensive than producing it in the United States, but efforts were made to become more self-sufficient and to compete with the British prices. Three primary sites in Kentucky, the Great Saltpetre Cave, Mammoth Cave in Edmonson County, and Saltpetre Cave in Carter County, became places of enormous expenditure of capital and labor in an effort to extract the named substance from these caves' floors. The product of these places became especially vital when the U.S. re-entered war with England in 1812. Once that conflict ended, purchasing gunpowder from England again became more economical than producing it stateside, and these caves ceased to be important industrial facilities. The property's second period of importance began with its purchase and establishment as a significant tourist attraction in 1938, a use that continued through the 1970s. This nomination uses information from both of the cave nominations named above in constructing its historic context narratives. The nomination of Mammoth Cave claims only Criterion A , and provides information on both of the Great Saltpetre Cave's Periods of Significance. The nomination of Saltpeter Cave in Carter County approaches that resource as an archaeological site, claiming both Criteria A and D. All three caves have retained many features, both on the ground and below-ground, from their use as industrial facilities. These caves' promoters pointed to these features when turning them into tourist sites. Because Great Saltpetre Cave 's archaeological exploration has been sporadic, its eligibility for Criterion D is conceivable, but not yet sufficiently explored to support this nomination under that Criterion.