I loved this book when I read it, but there is a small inconsistency here. The cave Axel mentioned was the Cueva del Guácharo, which is located in Venezuela, and by the late 19th century, Venezuela already existed as a country per se. I don't like to use Wikipedia for quotes, but here's the info anyway. https://en.wikipedia.org/wiki/Cueva_del_Gu%C3%A1charo_National_Park