The Casto Hole is a cave hidden by the woods, located near Limber's Ridge on the waters of Straight Run, a branch of the Tug Fork of Mill Creek in Jackson County. It was a Unionist refuge during the Civil War and achieved notoriety in the scurrilous contemporary ballad, "The Casto Hole," by Elihugh Powers. It has since become a part of local historical lore.

Jackson and adjacent counties were mostly loyal to the Union, and a Tug Fork Home Guard militia was established to protect the local citizens and their homes from Confederate scouts and raiding parties. The Home Guard held meetings in the Casto Hole. At times of threat Unionists would go there for safety, and it has been said that runaway slaves could find refuge there. Nicholas Casto was elected captain of the local Home Guards.

Elihugh Powers, a prominent resident, was a Southern sympathizer. This prompted Nicholas Casto to write a poem, now lost to time, critical of the rebellious Southern states and censuring Powers for his belief in their cause. Powers responded with enthusiasm when he penned "The Casto Hole." Originally 27 verses, over time it was reduced to 19. It ridiculed the people and activities at the Casto Hole and stirred strong emotions in the county. High-tempered Casto youths wanted to tar and feather Powers, but calmer counsel prevailed. As time passed, the song came to be taken with more humor than hostility and some members of the Casto family were even said to laughingly recite some of the verses.