Visit a place where an important event took place. The Boston Massacre site is where the legendary conflict between the colonists and British soldiers took place; some would even say that this event was one of the many catalysts to the American Revolution.
Spend some time hanging out in the country's oldest park. The 50-acre Boston Common is the anchor for the Emerald Necklace park system and is the starting place of the famous Freedom Trail. There are quite a few monuments throughout the park, and several outdoor events take place in the Common throughout the year.