Marengo Cave in Marengo, Indiana, is a privately owned show cave and one of only four in the state. Discovered in 1883 by the Hiestand siblings, Orris and Blanche, it opened to public tours within days and became known for striking mineral formations. Early protection by landowner Samuel Stewart helped preserve notable sections such as the Pillared Palace, Queen's Palace, and Crystal Palace. The cave remained in the Stewart family until 1955, later expanded under new ownership after 1973. A major 1992 breakthrough added about 3.5 miles to the known system and revealed Indiana's largest known cave room. It was designated a National Natural Landmark in 1984.