A limestone quarry on the east side of Hellertown, Pennsylvania, cut into this cave in 1883, which is how most of the show caves in this part of the country were found: not by explorers, but by people digging rock for something else.
It consists of five chambers, formed by karstification, the slow dissolving of limestone by water working along joints in the rock. It has gone by other names in its time, including Rentzheimer's Cave and simply Lost Cave.
The name that stuck belongs to the water. A river runs through the cave, and nobody has ever established where it comes from or where it goes. Its source and its mouth are both undiscovered, which is why it is the Lost River. Dye tracing and exploration have not resolved it, and the passages that would answer the question are too tight to follow.
The cave holds a consistent 52 degrees Fahrenheit whatever the season, which in the days before refrigeration made caves like this genuinely useful and not merely interesting.
It is a small site and unpretentious about it. There is a gift shop and a museum before the entrance, holding a collection of minerals, fossils and mounted specimens, and the tour through the five chambers is short, guided and easy going. The cave has been in the same family's hands for generations, which shows in the way it is run.
It sits close enough to Bethlehem and Allentown to be an afternoon rather than an expedition, and it pairs naturally with Crystal Cave, about 25 miles west near Kutztown, if you want two of Pennsylvania's oldest show caves in one day.
Other places on the map within a couple of hours.
