Portsmouth, NH. Market Square, Prescott Park/Strawbery Banke. It's only a mile off I-95.
Day of week and time of day really dictate the route you take and where you pick to stop along the way. There are a lot of fierce traffic jams to be found all along that route. Northbound I-95 in New Hampshire & southern Maine is a mess on Friday night and Saturday. Southbound is a mess on Sundays. The Boston midweek rush hour goes from 3pm to 7:30pm and it's worst on Fridays. I-95 in Connecticut is brutal during rush hour. I-84 west of Hartford is almost as bad.