Places to take a new graduate in the Baltimore/DC area

Quid

Next week my little brother in law is going to be visiting us for a week and change as part of his high school graduation present. I've got the whole time off and am looking for suggestions besides the obvious. But the thing is my wife and I are also both still kind of new to the area and only really know the obvious too. There will probably be at least a couple trips down to DC to visit all the monuments and museums as well as the museum at the Naval Academy. But besides that stuff I'm not sure where else to take him. I know he likes museums and physical activities like hiking. I'm a fan of both too but especially with the latter am clueless about where to look. The summer heat doesn't help any either.

But also if there's some place that's awesome or even just really weird that gets overlooked it would be great.

BlochWave

The Aquarium in Baltimore's Inner Harbor should probably be on the "obvious" list too. Not free though, but well worth it. When I went you had to buy a ticket several hours in advance, so plan ahead. I can't in good conscience let you go to Baltimore and not recommend Miss Shirley's restaurant. Little Italy is also in walking distance of the Inner Harbor and sort of a neat stroll with good places to eat (guess what kind).

If he likes aerospace even the slightest, and most likely even if he doesn't, the trip out to the Dulles annex of the Smithsonian Air and Space Museum is well worth it. Like the other Smithsonians, it's free, but there is a charge for parking. That's where they keep the big stuff like the shuttle orbiter, SR-71 Blackbird, and Enola Gay (and countless other things).

While you're out west, Dulles is on the way to Luray Caverns (maybe go alllll the way out to Luray, then start coming back in). That's a pretty long drive, and your time is limited, but if you're already in Dulles it might not be too bad (and again, if museums are your thing, you haven't been to "the Air and Space Museum" until you've been to the Dulles one). Co-located with Luray Caverns is a pretty neat old car museum. Also out there are places like Front Royal and Leesburg, but I don't know that wandering around towns is something he'd like and worth your limited time (but if you and your wife want something to do some weekend there's a place in Leesburg that has deeeelicious pie). Frederick, MD, and Alexandria, VA also fall in that category. Alexandria is accessible via metro though, and less of a commitment, time-wise.

Great Fall Nationals Park/Carderock is very close to DC, and offers options as far as a pleasant day hike along the Potomac (don't get in the water there! It's deadly fast). Think he'd like rock climbing as a gift? A few local rock climbing places offer introductory outdoor classes out there.