Steven F. Udvar-Hazy Center (National Air and Space Museum)
This remarkable museum, located 45 minutes west of D.C. near Dulles Airport, opened at the end of 2003 as a companion to the hugely popular and overcrowded National Air and Space Museum on the Mall. But it is in fact a far superior endeavor in almost every way. This museum has a huge amount of space all to itself in the middle of nowhere, and it revels in it. The massive, three-level hangar is like a zoo for flying machines: the Enola Gay, the Space Shuttle Enterprise, the Lockheed SR-71 Blackbird and the Concord are all here, to name just a few. Free tours are offered daily. Bring sandwiches from Firehook Bakery or Marvelous Market (both have various locations around D.C.) to avoid having to eat the museum fast food.
Great Falls Park
There is something thrilling about the roar of water hitting rock, especially if you've spent the day gazing at tattered flags and proclamations. Great Falls Park is just 15 miles from D.C., but its 800 acres of trees, gorges and water are a good place to go for a hike or throw a frisbee without hitting any statues.
Shenandoah National Park
For a true wilderness experience, drive out to Shenandoah National Park, about two hours from D.C. in the Blue Ridge Mountains of Virginia. You can go biking, fishing or just drive along the scenic Skyline Drive, a popular fall-foliage expedition for locals. Shenandoah also has some excellent hikes, including 101 miles of the Appalachian Trail. You can make it a day trip or, if you really want to commune with nature, spend the night in one of the park's campgrounds. For a nicer bed and a fine dinner after a long day of exploring, make your way to the Joshua Wilton House.