A cavern just outside Harper's Ferry served as a hiding place for Confederate guerrilla raiders throughout the war

Gen. Philip Sheridan's soldiers were baffled by Confederate partisan ranger Col. John Singleton Mosby's skill at eluding arrest by vanishing from his pursuit in November 1864, during Sheridan's Shenandoah Valley campaign. A Federal cavalryman was scouting for insurgents when he fell down a trapdoor on the floor of a burned and abandoned building, making a surprising find close outside Harpers Ferry. There was a tunnel going to an underground staircase under the trapdoor.

The Federals returned with a scouting group and entered a tunnel that they thought could house 300 horses by descending the staircase into it. Only one entrance to the room existed, and it was so small that only one horse could pass through it at once and only after wading through three feet of water. The entrance was concealed by bushes and rocks, and the hideout was designated by a tall cliff. They immediately understood that the room belonged to Col. Mosby and his group of rangers, which allowed them to escape federal authorities' custody.