I used to travel to Boston quite often. For a while, I was spending almost half of my time there (the other half, I was in Salt Lake City). My favorite place to stay there was Holiday Inn on Beacon Street in Brookline. Hotel was OK, had decent breakfast and it was very close to Longwood Campus where I worked.
I had a number of running routes starting from that hotel, some shorter, some longer. The shortest one was just over 3 miles, while the longest one was over 10 miles (Boston sightseeing, Freedom Trail and the Boston Harbor). My most common running route, was this one I recorded on May 14, 2007.
From the hotel, I ran on Beacon Street towards the downtown, turned left on Mass Avenue and went across the Harvard Bridge over Charles River. On the other side, in Cambridge, I went left and ran along the river, crossed the Boston University Bridge, went around the Amory Playground and then back to the hotel. This route was about 4.2 miles. Most of it was on the streets, and even early in the morning there was significant traffic, but for being in the city it was not too bad. The part along the river was very nice.