The East Bank Esplanade that begins at the east end of the Steel Bridge isn't actually a rail trail, but it definitely provides some good train views. The pedestrian overpass there is right by the East Portland interlocking, where the line from Union Station links with the north-south UP main line. You'll see Amtrak, BNSF, Portland & Western and UP.

The esplanade connects to the downtown Portland waterfront park by a walkway on the lower, railroad level of the Steel Bridge.

If you follow the esplanade down past the Oregon Museum of Science and Industry (OMSI), you'll reach the north end of the Springwater Trail. This parallels the Oregon Pacific RR East Portland line all the way to the Sellwood neighborhood, then turns east to follow the old East Portland Traction ROW all the way to Gresham and Boring.

If you get over to Beaverton and Tigard, you can see where the new Westside Express Service (WES) regional rail line is going in.