UPDATE: Sunken Mine had been repaired! (visited in early December, 2023).
64 mile gravel route that starts in Cold Spring, loops around Fahnestock Park, and captures some additional gravel in the Garrison area. About 40% gravel by distance, but probably 50% or more in terms of time spent riding.
NOTE1: Boyd's Corner Store/Deli (near mile 30) is the *only* reliable place to get food and water beyond the very start and end of the route. Before you leave Boyd's, make sure you are well fed, have snacks, and your water bottles are full (gatorade and gallon jugs of water available to purchase)
NOTE2: This route has some killer climbs. If you are looking for a still-challenging, but less intense version of this route, see here: ridewithgps.com/routes/37003811
The alternative route (above link) has less gravel/dirt, adds a potential stop in Carmel Hamlet, and skips some of the more ridiculous hills.