Lost River Caverns is a natural limestone cave on the east side of Hellertown, Pennsylvania, notable for the underground stream that flows through it and whose source and mouth remain unknown. Formed by karstification, the gradual dissolving of limestone by water, the caverns now extend through five chambers. They were discovered in 1883 when a limestone quarry broke into the cave. Earlier known as Rentzheimer's Cave and Lost Cave, the site has long attracted visitors. One of its most distinctive features is its steady interior climate, which stays near 52 degrees Fahrenheit, or about 11 degrees Celsius, year-round.

Lower Saucon, Pennsylvania · USA