This is a beautiful loop made possible by the opening of the Cuomo Bridge bike path, and for those who like mixing it up and riding both roads and rail trails.
The loop takes 9W north to Nyack, then crosses the Mario Cuomo Bridge bike path to Tarrytown, ascends up to the Tarrytown Lakes Park, then returns south on the N/S County Rail Trail to Van Cortlandt Park continuing to the Hudson Bridge crossing and the Greenway bike path south to wherever you want to finish.
The loop also offers a number of options. Going north it's riders' choice such as River Road instead of 9W, and perhaps getting some extra climbing in over Bradley/Tweed on the way to Nyack.
But the big question is once over the Cuomo Bridge and in Tarrytown how to get up to the Tarrytown Lakes Park?! All the options involve pain (gravity), with some steep ramps thrown in. The three main artery roads up the hill are Prospect Ave, Benedict Ave, and the most direct and fastest way up, Neperan Road. However, they all have their share of traffic and no shoulder. So I looked for a more cycling-friendly option and definitely found it with Martling Avenue. Further, all of the roads on this route to the lake above Tarrytown are on back residential roads that go nowhere, so you’ll only see local traffic, if you see any cars at all. They are beautiful residential roads, quite wide, and including the lovely Hackley Campus. I was recently reminded Hackley is the prep school of the Koch brothers. So it’s like a biking car-free tour of lovely Tarrytown, ending up at the lake, with a couple of leg-burning ramps thrown in. Perfect.
Once up at the Tarrytown Lakes Park, a lovely bike path takes you around the lake and joins up with the N. County rail trail south.
NOTE: At mile 27, the route passes through the Hackley Campus. Once in the campus, you will take the first left and ride by a building on the left, then a parking lot, then take the next left. This is a short service road and you will see "Do Not Enter" signs. These signs are for vehicles. Bikes are fine to descend this 100 meter service road to exit the campus.
ALSO, after descending from the Hudson Bridge once back in Manhattan, there is a pedestrian bridge over the rail tracks that involves stairs on both sides.
RMS 9/4/2020