Longwood Gardens is one of the biggest attractions in the area and is absolutely stunning year round. If you have never been we definitely recommend it!
Winterthur is a combination of beautiful gardens, amazing walking and running trails and a Museum of Decorative Arts.
The Brandywine River Museum is a lovely art Museum right on the Brandywine River with three generations of Wyeths.
The Delaware Art Museum is a lovely local collection specializing in Delaware Valley Artists such as Howard Pyle and British Pre-Raphaelites.