Boston is a great place to visit. Park your car and take public transportation and do take the walking tour of the many historical sights. Once you're downtown you'll be within walking distance of of too many places to see in one day. Also, you might want to head over the Charles River to Cambridge and check out Harvard....food, shops, local color...unlimited experiences if you like a city experience. I have been there many times and I want to go back again and again.
If you have not traveled to the Southwest, Arizona is a very cool (but sometimes HOT) state to visit. It is one of those states that not only has a giant attraction (Grand Canyon) in the North, but as you drive south throughout the state there are just dozens of places to visit and scenery that never stops. Coming from the Mid-West, our first time in AZ was like coming to a foreign country. Of course, you'll want to stop in Flagstaff, Phoenix and on down to Tucson. Keep heading south to the wine country and rolling hills that will seem out of place after you have driven through the desert . If Arizona had an ocean, it would be the perfect place.