Spelunking is a word that refers to exploring or otherwise traversing caves. A Spelunker is an amateur cave explorer. Spelunking is considered a hobby or sport by some, like mountain climbing. The word spelunk left common usage in the English language around 1600 CE, but spelunker returned to the language in 1939 to refer to people exploring old mines or caves. Over the 1940s, it eventually became a relatively common word. By the 1960s it came to have the connotation of being an amateur cave explorer, whereas a "caver" is a more experienced or professional cave explorer.