Imagine that you traveled to the center of the world. But in this case, the world is a hollow, three-story, stained-glass orb. Built in the 1930s, the mapparium puts you inside a globe and allows you to remember how bad you were at geography. Also, it gets pretty freaky with acoustics: whisper sweet nothings in your date's ear and they might be heard by strangers at the other end of the globe.
9. Go to the library... for music
Here's a little known fact: in the summer, the main branch of the Boston Public Library hosts free one-hour concerts in its stunning central courtyard -- sometimes during lunch, sometimes in the evening. And we're not just talking classical music; jazz, blues, and folk have also appeared on the menu.
10. Walk the Greenway
So yeah, you'll stroll past some decidedly not free food trucks, but the 15-acre-long park takes you past Chinatown, water fountains, art installations, and a host of people watching opportunities. All of which is free. When you're done, hop over to the Harbor Walk for your return voyage.