[…] I discovered this particular one to be merely a shallow recess in the limestone, nowhere reëntrant to a distance of over forty feet, of the general proportions of a tin oven, and transacting an immense business of mystery (or what they call, as far west as this, "Shenandigan" and "Scullduggery") with those who gape at it from below, on the capital of a dark, overgrown portal, as big as the cave itself.
Source: wiktionary