While not in the Simsbury area, since CT is rather small, here's what I can think of from my neck of the woods (south-central to southeast CT):
- There's unobstructed (read: no fencing) view of (what's left of) Cedar Hill Yard on Universal Drive in New Haven, just off of I-91 exit 9, in the southern parking lot of the P.C. Richards & Son. It's right near where CSX lays up their engines, too. Been here numerous times, and I've never had any trouble; of course, since there's no fencing, just remember not to tresspass on RR property.
- Old Saybrook, as previously mentioned; probably one of the most popular places on the Shore Line for photography. The 1873 station is still there and in-use as a ticket office and waiting room, and you can see how the Valley Line continued southward because of its odd shape. The restaurant Pizza Works is in the old freight house, which is convenient as well. Also nearby the station is Amtrak's Connecticut River Bridge; there's a park on the Old Lyme end of it, including a boardwalk that runs underneath it, and is all-around a good place to watch the movable span operate in addition to trains. The 1907 bridge is visibly in not good condition (in addition to breaking down fairly often), so it's days are numbered (the replacement project is in its design phase now, I believe, so it's still going to be there for a while).
- Essex is definitely something you should see, as that's where the Valley Railroad bases their excursions out of. Only place nearby you'll see operating steam locomotives! There's a number of well preserved stations along the Valley Line there, and it's a very pretty area, so definitely check it out sometime! (Totally not biased by having done volunteer work there )
- Niantic in East Lyme is a neat place; there's the new replacement bascule over the river on the east side, and a boardwalk flanks the Shore Line along the beach and cove. Really wide view of the railway because of the cove, and all-around pretty.
- New London Union Station is finally also a good place to visit. Shore Line East terminates some trains here, and Amtrak stops as well; well-preserved station, right on the Thames River. It's also truly a multimodal station, with three ferries (Cross-Sound/Long Island, Fishers Island, Block Island), as well as the local city busses. There's also a boardwalk here, too, and at the south of it there's a swing bridge over Shaw Cove that is easily viewable. If you're doing photography/videography, Amtrak Police might tell you (politely) to just not do it on the station property/platforms (the one time this happened to me, the guy basically just told me to just go to the areas just beyond the crossing gates).
More in your area of the woods and also elaborating on others' thoughts, you should check out Pan Am Southern's (jointly owned by Pan Am Railway/Norfolk Southern) Waterbury Branch; the previously-mentioned EDPL/PLED runs between E
eerfield (MA) and Pl
ainville. Going west of Plainville, there's Terryville, which hosts a number of interesting features. There's the Terryville Tunnel, one of the few (remaining) tunnels in Connecticut. No easily accessible place to view the portals, but since there are roads right above both portals, I've seen photos and video from people who've been able to scale their way partially down the embankments to get their shots... obviously do so at your own risk and judgement. And then there's the spur up to Firestone; there's very large loop at the bottom of the spur to wind its way upwards (which is a remnant of the original pre-tunnel alignment) and sports an freighthouse
(in commercial use), which is right next to a wood trestle (offscreen to the left in that streetview panorama). Still going west to the end of the Waterbury Branch, Waterbury itself is an... iffy city, to say the least. The old station there is home to the Republican-American newspaper, and the MNRR station is right below it where the Waterbury Branch trains terminate, but the parking area along the station has had a tendency to have (the commuter's unattended-to) cars in it broken into in some areas where there's no sightline from the street below, so I can hardly recommend it as a "good" area to see. North of there in Thompson, though, is the Railroad Museum of New England (which is more excursion railroad than museum), so that's also a place to also check out. They also do some limited freight moves, as well.
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