Lost River Caverns is a natural limestone cavern 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 Cave and Lost Cave. 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.
Tours are guided, and payment is upon exiting the cavern. The Lost River Caverns is not hazardous from rock falls because all of the rocks are covered with a natural rock cement, preventing rocks from falling. The rock path may be slippery from dripping water, though.
It was discovered in 1883 when a limestone quarry cut into it. It is currently open to the public.(Wikipedia)