From the falls lake damn, you can ride the Greenway all the way to Clayton. That works out to be ~28 miles each way. The Greenway is busiest near the damn, first 2-3 miles can be irritating with oblivious people on the wrong side etc. It can be a little busy around the soccer complex at mile 6.5, but it won't be as busy. There are bathroom at Andersen Point park around mile 17.5. The most scenic parts are between Andersen pont and Clayton, at least that is what I think. I ride the Greenway 2-3 times a week and see people on TT bikes, but the responsible ones sit upright when people are on the trail. On nice, warm spring days parking at the lot by the damn can be tricky after 9am, but there are a ton of other less popular entrances.