Pierceton has a nice brick station. Last I knew, it was being turned into a restaurant, complete with passenger car on the east side.
Warsaw's station, last used by Amtrak, is now a kid's clothing shop. It's on the north side of the track between Lake & Washington Streets.
Plymouth's station is in the NE quadrant of the diamond with the former Nickel Plate, and is still used by NS MoW forces last I knew.
The station at Hobart still stands as well, but I can't recall exactly where it is located.
There's a really neat stone arch bridge in Columbia City, but it's rather difficult to see/photograph this time of year due to the foliage. Take Highway 9/205 to the south side of town for a glimpse of it.
The bridge over US 30 on the east side of Valparaiso still has PRR keystone logos in the concrete. Neat to see, but difficult to safely photograph.
Other than that, there are PRR position light signals at Warsaw, Plymouth, and Hanna diamonds, as well as the distant signals for these diamonds. Can't really think of anything else "must see" along this line