Extension of Trenton/New Hope-Lambertville/Trenton route. Ridden hard, this is a very good workout for all levels as gravel surfaces offer resistance, and there are few interuptions. Winds can blow up and down the river valley. In fair weather winds tend to be on your tail on the return.
I rode it solo yesterday with strong headwinds out and tailwind on return, stopping only for pictures and a can of coconut juice. Riding time was 3:45; YMMV.
Plenty of opportunities for food/fluids and restrooms. But no bailouts to trains.
Trains from NYC Penn Station run hourly, riding time 90 minutes each way. 2 bikes can be carried on either end of the double decker train cars, flipping seats up. You can secure your bikes with thin rope, sitting on seats across the aisle. Train begins at NYC Penn and ends at Trenton so you will not be rushed on and off. NJ Transit does not require a bike permit; one less hassle!
Online NJ Transit schedule: http://www.njtransit.com/sf/sf_servlet.srv?hdnPageAction=TrainTo
Note that NJ Transit senior ticket discount starts at age 62. Bring ID.
Except for access to the towpaths, you will only deal with motor traffic when roads cross the paths. The towpath surfaces are gravel. It is friendly to road bikes but wider tires are a nicer option if you have them. There is even a path going over Rt 29 on the NJ side at Washington Crossing State Park.
Caution is needed when passing under bridges while cycling north on the Delaware Canal towpaths (Pensylvania side.) Be sure to gauge headroom as these vary. If in doubt either walk your bike or ride to the right and cross the road off the bridge. Also, there are a few blind spots as you approach these underpasses. Be wary and respectful of oncoming path users. Another issue is crossing spillways on the Delaware Canal towpath (in Pennsylvania.) There will be times that some water will be spilling over them. Unless there have been recent rain of biblical proportions, you should easily be able to cycle thru these. The surfaces on these spillways are concrete; the surface is very rideable.
Landscape, architecture, and historical canal infrastructure, along with great rideablity of these trails make this a worthwhile addition to your cycling CV.