We went to the Morris Arboretum in Chestnut Hill today. It was much better than I expected and it's so close to our house! You could really get into all the nature stuff, or just enjoy the beautiful landscapes and walking trails. We did the latter and Ben even enjoyed eating in the rose garden and seeing some ducks in a pond. We'd recommend it, especially for kids older than Ben who can run around and learn a little bit at the same time.