Steamtown is a bit of a hike from Baltimore.
Baltimore has some nice rail fan spots, unfortunately some of them will get you shot going to.
St. Denis MARC station (Camden line) and Relay sit right where the Old Main Line splits from the Capital Subdivision. Weekdays have freight and passenger trains, weekends have freight only. On weekdays during warmer months, CSX maintainers will take some of the tracks out of service during the mid-day period, returning them to service around 2:30-3:00 usually. If your into train pictures, St. Denis is an all day stop (westbounds in the AM, Eastbounds in the PM).
Bailey's Wye is located in a fairly safe part of Baltimore, near the stadiums. Bailey's Wye is pretty busy, as all traffic passes through it (northbound into the Howard St Tunnel, southbound down to St. Denis and eastbound to the marine terminals) Keep your eyes open though, but I doubt you'll run into much trouble. Avoid going if it's an O's home game.
There are various CSX stops north of Baltimore on the Philadelphia subdivision, but none I'm too familiar with.
Amtrak wise, Halethorpe in southern Baltimore is on a 100mph straight away, so you can get some nice shots. It's low platforms with no real separation, so beware of trains at all times.
North of Halethorpe the line heads through West Baltimore, which is not the nicest place on Earth ( a lot of The Wire was shot there) so I would say no go for that.
Penn Station is a restricted area so you won't be able to get to track level unless you buy a ticket, or use the light rail platform.
Heading east, Amtrak travels through the Union tunnels and out into East Baltimore, which is just as bad as south Baltimore. Avoid, plus the tracks run elevated for a while.
Edgewood, Martin's Airport and Aberdeen MARC stations are good for Amtrak trains.
Martin's Airport has an automatic signal facing you, so you'll be able to know what tracks will go with what direction. These are only block occupancy signals, so they may be green for a very long time, but if you see a red stop signal, it means a train will be coming the opposite direction on that track at some point. A red signal with a white light under it means a train just passed.
There is the Canton railroad, I can't speak much on that.
Norfolk Southern has a yard in Baltimore, but they have police there. I've heard it's not very rail fan friendly, and parking isn't that great.
Thats Baltimore.
-Greg Primrose
Co-Owner, Railroad.Net
Ave Atque Vale