Callaway County, US
Research Cave, also known as the Arnold Research Cave and the Saltpetre Cave, and designated by the Smithsonian trinomial 23CY64, is a major Native American archaeological site near Portland, Missouri. Investigation of the site has uncovered evidence of human habitation as far back as 8,000 years. T
he site was designated a National Historic Landmark in 1964; it has been recommended for de-designation due to looting.
Listen to the audio guide for Research Cave Free on WIP — starts by itself when you arrive, even with the screen off