What's the best natural wonder to visit while in Beacon for someone who isn't super duper athletic?

There are four hikes right around Beacon, but if you don't want one that's too strenuous, I'd go to Dennings Point, which has a 45-minute walk on mostly level ground that takes you right down to the river. Follow the white trail markers. It's a really nice outing, and you'll be able to see Bannerman's Island and Newburgh. First go to the Beacon Institute of Rivers and Estuaries, on Main Street, and pick up a couple of trail maps. The people in there are really friendly and helpful and know the area like the back of their hands. Maybe you'll be inspired to take a longer hike next time!