Grottoes is an incorporated town in Augusta and Rockingham counties in the U.S. state of Virginia. The population was 2,668 at the 2010 census.The Rockingham County portion of Grottoes is part of the Harrisonburg Metropolitan Statistical Area, while the small portion that extends into Augusta County is part of the Staunton?Waynesboro Micropolitan Statistical Area. Only seven of the town's 2,668 residents reside in Augusta County.Grottoes is home to the Grand Caverns, America's oldest show cave.