George Carter, a great-grandson of legendary planter Robert "King" Carter of the Northern Neck, built this mansion in the Federal style in 1804 but later converted it to the Greek Revival manse we see today. His formal terraced garden and its 1810 propagation greenhouse -- it's considered America's second oldest -- are as interesting as the mansion itself. The plantation's remaining 330 acres also contain unique tree species. Now operated by the National Trust for Historic Preservation, Oatlands hosts numerous events, such as the Antiques at Oatlands show, sanctioned sheepdog trials, a bridal fair, and an American-crafts show (call or check the website for the schedule), plus private events. From mid-November through December, the mansion is all decked out for its annual holiday candlelight tours. You must take a tour to see the house, but you can wander the gardens on your own.