In 1861, the owners shut down this iron furnace to form Company E of the 27th Ohio Volunteer Infantry and fight in the Civil War. The operation resumed when they returned in 1863. One of the workers was struck by lightning and killed while seeking shelter from a storm under a nearby maple tree.

Not only is the Keystone Furnace rich in history, it's also a very unique structure. The builders carved it out of a solid sandstone cliff. Pick marks are visible on the interior walls. The tunnels really set Keystone apart from the other iron furnaces in Ohio.