Longwood Gardens is a beautifully landscaped botanical gardens, conservatory, and estate located in Kennett Square, PA. Originally owned by the DuPont family, Longwood is a world-class horticultural center. LG has everything from organic gardening displays to hydroponic exhibits to a brand new children's garden. A ton of walking trails snake through the entire estate; I think my favorite part is the huge wildflower meadow at the back of the estate. Fountain shows synchronized to music are regularly occurring, and fireworks displays take place several times a year. During the summer, they also have a free concert series.
The price of admission is a little expensive, but it's well worth it for an entire day at Longwood!