Maybe Annapolis, MD (would fall in the detour category)
I can't categorize anything as a "must-see" unless the subject matter of either of the two places below suits your interest. Mostly you'll find small shopping centers along the way if you choose to take the commercial route (U.S. route 1) or an attractive tree-lined route if you take the Baltimore-Washington Parkway. Otherwise, take the less-leisurely superhighway (I-95) and make do with the extra time you'll have on your hands in Baltimore.
There is a decent small aviation museum at the historic College Park Airport. www.collegeparkaviationmuseum.com/home.htm A lot of hands-on exhibits that are especially good for kids, but adults will find it interesting as well.
The National Cryptologic Museum is also along the way--I haven't seen it personally, but I have heard good things if that interests you, and it's on my list when I have the time.
Annapolis is a good suggestion and would be more of a must-see for those with general interest than the above attractions. But it is definitely a detour vs. en route--although it sounds like you have the time on your hands.Edited: 03 May 2011, 14:45
Thank you both for your input! We are visiting Annapolis after Baltimore, on our way to St Michaels, but the The National Cryptologic Museum sounds like an interesting stop en route.
Always provided we are not totally museumed-out after Washington!
Arundel Mills outlet mall is just off your route if you want to do some shopping.
Depending on time of day you may stop whether you want or not. Other than some govt museums not much to stop for on a straight line. It is only an hour door to door.
The town of Laurel, MD is right off I-95 and quite charming:
hundreds of thousands of people pass right by Laurel every day without stopping and they can't all be wrong. :) I'd call it a "maybe if you have nothing better to do see"
I've got to say I've never found much in Laurel to recommend a visit. They have a "historic" Main Street with some period light poles and that type of thing but nothing I can think of to draw a strolling visitor looking for a break from the road. They do have some older homes in their historic district.
Ellicott City, on the other hand, is worth a stop if you're into shopping and nibbling. Main Street in Ellicott City would be about a 15 minute detour from the main route between DC and Baltimore and is worth an hour or more for lunch and some browsing if that's what you're looking for.
If you're into antiques at all, and a shorter detour from the main road, check out Savage Mill. Stores and a good beer tavern (Ram's Head) and a really good bakery (Bonaparte Breads) that I can never pass by without buying something).
Oh, and you can do zip lining there too!
Irish and I agree again! Ellicott City is not a "must see" but its pretty close! The B&O Train Museum is there. The quaint little town has very steep hills and reminds me a lot of Cumberland, MD. Antiques shopping is the prime activity here.
Its actually on the south side of Baltimore but I'd definitely say Fort McHenry is a must see.
Between Baltimore and Washington, I'd say the Annapolis detour would be the only thing and it is quite a detour. But you say you're going there anyway, so I would say skip Laurel, DEFINITELY skip the Washington area outlet stores, they are a boring rip-off, just spend more of your time in Washington. If hands-on science exhibits interest you, Maryland Science Center is right on the Inner Harbor in Baltimore. You can lay down on a genuine bed of nails!