Nature Bank

Luray Caverns  is a large, celebrated commercial cave just west of Luray, Virginia, USA, which has drawn many visitors since its discovery in 1878. Luray Caverns does not date beyond the Tertiary period, though carved from the Silurian limestone. At some period, niches and already formed chambers were completely filled with water, highly charged with acid, which then slowly began to eat away at much of the softer material composing much of the walls.  Source