I thought Ohio had numerous covered bridges??
And old barns??
Honestly neither of those things would merit a stop for me :-). Some of my rides last were silly but fun stuff like riding 200+ miles to hit every Harbor Freight in a 50 mile radius to get multiples of a flashlight that I liked plus a "free" 24" magnetic tool rack. Part of the challenge was to NOT give a phone number so that I never got tagged in their system as having already bought the "limit one" flashlight or used the coupon for the "free" magnet bar. My Windjammer ended up PACKED with HF goodies by the time I had hit 4 stores over 200+ miles :-). Each "win" at not giving a phone number spurred me to map out my way to the NEXT store. I hit Defiance, OH, went down the river to Maumee, OH, then to Fort Wayne, IN and finally Auburn, IN. Probably no other reason would happen to spur me to hit those 4 urban centers in one day LOL.
I might start a thread on the "scavenger hunt" stuff like that this coming summer, to me the ATT longlines stuff is really cool cold war leftover stuff that is not difficult to find. They also run along a route due to being line of sight coms which required towers to deal with the curvature of the planet we live on :-).
Ditto on the air mail route beacons or even just their GPS locations. Thinking maybe about maybe leaving GeoCaches near some of those locations :-). That might create a way to flesh out the history of others who decided to visit or stop on the way by too. I'd be more likely to stop at an old barn or a covered bridge maybe then :-).
I have also gotten into the habit of NOT just riding past the "historical markers", I more typically stop and read them. Then there are things you just discover like an RC airplane field that was filled with devotees flying their planes :-).
Bill