Indian Echo Caverns

Indian Echo Caverns is a show cave in Derry Township (Dauphin County) near Hummelstown, Pennsylvania, USA. The limestone caves are open for the public to visit via guided tour.
The entrance to the caverns used by modern visitors is located in a bluff along the Swatara Creek. A second entrance was sealed for security purposes when the caverns were commercialized in the late 1920s. The known portions of the caverns, most of which have been commercialized, represent the intersection of two passages: the "eastern" cavern and the "northern" cavern, which meet at right angles to form a large space known as the "Indian Ballroom."
Given the large and accessible natural openings the caverns were likely utilized by Native Americans for storage and shelter, however no evidence of such use has survived. The location was previously known as Wilson Cave, Hummelstown Cave, Stoverdale Cave, Giant's Cave, and Indian Cave. When it was commercialized it was renamed Indian Echo Cave. It has more recently been known as Indian Echo "Caverns". 
For nineteen years (1802–1821) the caverns were the home of William Wilson, known as the Pennsylvania Hermit. Wilson withdrew from society after his failure to halt the execution of his sister Elizabeth for the murder of her twin sons. Following her death in Chester, Pennsylvania in 1786, William wandered westward across southeastern Pennsylvania, settling in the caverns in 1802. "The Sweets of Solitude: Instructions to Mankind How They May Be Happy in a Miserable World", an essay supposedly written by Wilson during his time in the caverns, was published following his death.
The same geological system of which the caverns are a part is responsible for many sinkholes in an area stretching from Hummelstown to as far as Palmyra, and as far south as Middletown.