The Great Manhattan Bridge Walk is a 27 mile walk that goes over all the bridges that one can leave Manhattan Island on foot. I will not be able to make it this year as it is a week from Saturday, but it is definitely on my bucket list now.
This event is hosted by Shorewalkers, the same organization that hosts the Great Saunter. They appear to be a very active organization - looking at their calendar they have many walks planned. It is stating the obvious, but you really do see so much more on walks like these versus driving through an area.
It does not matter if it's urban hiking or nature hiking - it's just good to get out there.