Nemours is the most ornate of the Brandywine du Pont estates, a 47,000-square-foot Louis XVI mansion set in the largest French formal garden in North America. Alfred I. du Pont built it in 1909 — partly to outdo his cousin Pierre at Longwood, partly because his second wife wanted a Versailles of her own.
The interior is exactly as the du Ponts left it, with original furniture, paintings, tapestries, and a notable collection of Louis XV and XVI decorative arts. The garden axis runs almost a kilometre from the house down to a Temple of Love, with a long canal, fountains, and a colonnade modelled on the one at Versailles. The greenhouse and the chauffeur's garage (full of vintage cars) are both worth a look.
Tours run on a timed-entry basis. Allow most of a day, especially if combining with the garden walk.