Sometimes it's fascinating to see how little some things have changed in parts of Boston. This is Park Street in 1858:
With the exception of the towers in the background, I think the only alteration to the built form that would be visible in the same view today is the former Curious Liquids Cafe / current Fox 25 News booth on the corner.
On the other hand, the North End looked surprisingly different in the 19th century. There seem to have been a lot of wooden buildings left over from the colonial period, and lots of Federal-style rowhouses. It seems a lot of it must have been rebuilt during the immigrant rush of the early 20th century.
And...whoa...this is the Washington/Summer/Winter intersection in 1846: