Shorpy — "the 100-year-old photo blog" — has a category called "Boats & Bridges." One of my favorite pics there is one of two riverboats called "Old Man River," taken in 1900.
The picture is so large and so high-resolution that you almost feel like you've been transported back in time. I find it strangely relaxing.
Click the pic to see the super-extra-large version.