Wynnewood, also known as Castalian Springs, is a historic estate in Castalian Springs, Sumner County, Tennessee. The property is owned by the state of Tennessee and its official name is the Wynnewood State Historic Site, it includes an 1828 former inn that is the largest existing log structure in Tennessee. The property is operated by the Historic Castalian Springs under an agreement with the Tennessee Historical Commission. It was designated a National Historic Landmark in 1971.