Portland can be quite full of action with the Amtrak facility, switchers going out to Westbrook, Deering Jct. and Yard 8, and freight trains going in and out of Rigby Yard in South Portland. Take a look around when you come.
I also have a power-point, Railroads of Southern Maine with pictures and directions to some of the other rail-fan sites. If your browser does not play it right try downloading it, and playing it in a PowerPoint program.