If you have ever read “a walk in the woods” by bill bryson he describes the trail as “a green tunnel.”
In thinking of it that way, he missed a lot of things that were just beyond that wall. I’ve ridden PGH-DC six times with plenty of other shorter rides and have not been really bored. Starting with the Companion book is a good start because it tells you plenty of things to be on the look out for. But really, you need to keep your eyes open and wonder.
For example, have you noticed the posts on the side of the trail between Rockwood and Garrett? They are marking geology highlights for a course developed for the local school district. The post marked F-GR5 (mile 40.7) is the Wymps Gap Fossil Quarry. Dig around in the hillside and you’ll easily find 330 million year old shells. Lots of shells. Coral is trickier to find. There should be trilobites but I haven’t found any yet.