If you go through Inwood Hill Park, you will need to carry your bike up and down some difficult stairs. I've done it with a 50 pound bike, and it was hard. Then there are very steep hills leading to the Henry Hudson Bridge. Then the bridge has a very narrow path. I'm able to cycle it even though the signs say we're supposed to walk our bikes. When an oncoming pedestrian comes, I grab onto a rail and stay still and let the person pass, as it's quite narrow. The view is spectacular, however. Then once you're in the Bronx, you'll have some more hills. The route I gave you above is much flatter. The worst part of it is the Broadway Bridge. The surface is a grate which makes noise. Traffic is loud, and it resonates against the upper level where the #1 train is. When the train moves overhead, it's extremely loud. All this noise is nerve wracking, but I don't think there is any big danger. It just feels like it. It is my un-favorite-est part of the commute.

Sorry, I was wrong above. I switched Riverside Dr and Dyckman St. Dyckman is the one farther north. That is where the new ramp puts you. Take Dyckman east, Left on Seaman, and turn Right at the end onto 218 St. Turn left onto Broadway. You may want to take a route parallel to Broadway once you are in the Bronx only because Broadway is so loud and unpleasant.

Here is a picture I shot from the Henry Hudson Bridge.