Archeologists on a mission to see where a mysterious passageway under the world's longest known cave system goes are uncovering 19th and 20th-century artifacts in the historical dig. This collapsed sinkhole, the largest known natural entrance to the Mammoth Cave system, is believed by researchers to be where the cave's extensive labyrinth of naturally formed passages first began at Mammoth Cave National Park in Kentucky. Archeologists from the National Park Service and the University of Idaho found artifacts — including coke bottles, ticket stubs, ceramic pieces and other items from over 200 years ago, according to Bowling Green Daily news. Click the link in our bio for the full story. 📷: Grace Ramey, @apnews