Visit the Walters Museum, formerly known as the Walters Art Gallery. On that excursion you can take a pleasant walk around Mount Vernon Place and see Baltimore’s Washington monument. One block west you can see the Basilica of the Assumption, the first cathedral in the USA. You can do “Ride the Ducks,” a combination of tour bus and boat, or take a trolley bus ride. I’d recommend doing things related to Poe and to John Waters, but only if those things really interest you. Not sure if Poe’s grave is on a standard Baltimore commercial tour agenda. If this is the only place in Maryland you’re visiting, eat steamed blue crabs. Look at citypaper.com for its events calendar. That site also has an archive of CityPaper’s “Best of” issues that might give you some offbeat to-do ideas. CityPaper is a free weekly paper that you can pick up anywhere. Taking Maryland public buses is perhaps an unpleasant experience, but it can be educational, and you won’t be with many other tourists. There’s a big visitor’s center right at the harbor.