We highly recommend the FREE Smithsonian Museums at the National Mall! Some require to attain tickets beforehand, such as the Air and Space Museum, but others are able to be seen without! Also, we got engaged at the National Gallery of Art if you want to check it out :)
The Inner Harbor is a gem! We love the National Aquarium (half-off tickets on Fridays after 5:00 pm), the Bird's Eye View from the World Trade Center (the tallest pentagonal building in the world), the shops (so much Maryland merchandise!), the dining, the histroy, and the views! Note: Baltimore is about an hour away from the Rockwood Manor.
Old Ellicott City is one of a kind! It is the home to 80+ one-of-a-kind small businesses and has been up-and-running since the early 1800's. We have gone countless times and love its unique charm, good food, and immaculate vibes. You need to check this place out!