Lost River Caverns is a natural limestonecavern consisting of 5 chambers. The caverns were formed by the karstification or dissolving of the limestone by water. In the past the caverns have been called Rentzheimer's Caveand Lost Cave.[1] The "Lost River", so named because the source and mouth of the river have not yet been discovered, flows through it. The caverns are located on the east side of Hellertown, Pennsylvania, United States. The temperature in the cave is consistently in the 52 °F (11 °C) area. There is a gift shop and a museum before the entrance.