If you're strictly a commuter/passenger train fan, the Western Ave station on Metra's Milwaukee/NCS district lines is a great place to visit, especially during rush hours. The station lies just west of the tower at A-2 crossing, where Metra's Union Pacific West line crosses this route. In addition to the regular Metra trains stopping there, there are also many equipment moves between Union Station and Western Ave yard, just west of the station. The majority of the moves can either be seen just after the AM rush as trains head to the yard for midday storage or servicing, or in the mid-to-late afternoon as the trains head down to Union Station to pick up passengers for the evening ride home.
Meanwhile, not far from Western Ave's south (inbound) platform, the same scene is being played out nearby as rush hour equipment from all three of Metra's Union Pacific lines come and go out of the east end of their California yard, clattering across the A-2 diamonds going to and from OTC each morning and afternoon during the end of the AM and the start of the PM rush hours, with numerous light engine moves scattered throughout the day. Throw in Amtrak's presence on the Milwaukee/NCS line, with the daily Hiawatha trains and an Empire Builder in each direction, and you've got some serious action. The only drawback is that besides Amtrak, the only other variety in traffic is provided by a local freight job that can be seen during the day, although not at the same time every day. I have limited knowledge of this job, I do know that it uses an NS switcher at times for power from what I've observed, although I'm not sure if that is indeed the normally assigned locomotive, and it works a small industrial area on the Milwaukee/NCS line about a mile or so to the east. Otherwise, it's strictly a showcase of Metra's basic and ubiquitous diesel equipment, gallery bi-levels with either F40's or the newer MP36's providing the power.
As for accessibility, it's probably best to get there via train, plenty of Metra service is available from Union Station, most trains stop there. For those that choose to drive, be advised that parking is a bit tight at the station, it's a very small lot, although there's plenty of parking within a block or two of the station, but the surrounding neighborhood is a bit risky. Despite that, it's a paradise for passenger train junkies, well worth the visit...
--Dorian--