Hellertown, Pennsylvania -- Lost River Caverns is open all year round! Located in Hellertown PA. The Caverns have been open since 1930, Robert Gilman's grandparents opened the attraction to the public. It is 52 degrees all year round. Visitors will be taken on a guided tour throughout the caverns and following the tour, there is an amazing gift shop. The public is asked to leave the cave untouched. The only this that tour guides take out are the people they bring in.