I found a nice loop to the east of Pittsburgh: heading due east to the Beaver Run Reservoir, then going south to Greensburg before finally returning to Pittsburgh via Monroeville.
Most of the route is kind of bland, but the section near the Beaver Run Reservoir actually features some decent countryside scenery. I didn’t stop for pictures, because I was trying to abide by the cardinal rule of long bike rides: keeping stops short and infrequent. I do have a few pictures from a shorter previous ride out to the reservoir, though I don’t think they do the area justice.
It’s not very exciting, but this is a decently hard workout route, with (according to Strava) about 71 miles and 6,778 feet of elevation gain. Since this is Pittsburgh, there are no huge climbs, but the terrain is very much rolling, so you get in a lot of elevation gain by the time you’re done. The most difficult part is the initial section between Penn Hills and the reservoir.
I did this ride mostly on the three-digit highways out to the east. In general, to echo a piece of advice that I once heard about cycling in the area, the highways with triple-digit numbers are usually good for riding. The highways with double- and single-digit numbers are usually major arteries and should be avoided on bicycle.