The DisneySea Electric Railway runs between the New York Harbor section of American Waterfront and Port Discovery. Unlike the Western River Railroad in Tokyo Disneyland Park, the DisneySea railway has stations at both ends. This means it serves a practical purpose, acting as transportation between the two areas of the Park.
The American Waterfront station is hiding under a bridge near the Broadway Theater. It's not hard to find, but if you weren't looking for it you might walk right by it. Although the design of the Port Discovery station is a little more elaborate, the American Waterfront station has a red-brick charm all its own.
If the lines are not too long, I recommend riding the Electric Railway. It's a serene, no-thrills ride, and serves as a nice way to get a slightly elevated view of this area of the Park. Be aware that the trip is one-way only, so if you want to make a round trip you will need to disembark and get back on. In my experience lines are a little shorter at the Port Discovery station, so that might be the best place to board.
For more photos and information, visit the DisneySea Electric Railway page for Port Discovery.