Whether you have a green thumb or just love to bask in nature, you'll want to check out the National Arboretum before you bid D.C. adieu. Spring is one of the best times to visit, when the azaleas, rhododendrons, and native trees are in full bloom. Summer visitors will enjoy beds of colorful annuals and perennials. And any time of year, be sure to stroll through the Bonsai Pavilion, where you can see an amazing collection of Japanese and Chinese bonsai plants, some more than 400 years old. Bring along a picnic lunch and head to the spot where the original columns from the U.S. Capitol are located—you'll never forget the view.