While in Boston, I walked the entire 2.5-mile Freedom Trail. It is a nice walk except for avoiding all the street construction. I have to admit also, as a tourist, it is nice not to really have to check a map, but rather just follow a red brick path in the sidewalks. I previously posted photos of the Massachusetts State House and the Bunker Hill Monument. Here are a few more photos from sites and just views along the Freedom Trail.
A brief explanation of why I am posting the below photo. There is a T (subway) train station right below the Old State House, with an entrance through the building. As an engineer, I find this amazing. Consider how old the building is and the studies of the building that must have occurred to determine it could handle both the space being dug out of its foundation and also the ability to take vibrations from the subway and people going in and out of it.