There is the sky, which is all people's together.
Urban Park Rangers
The fall issue of the Urban Park Rangers' Outdoors in New York City is available—the link is to the PDF. It contains a smorgasbord of "Weekend Adventure" activities with something for everyone, including astronomy, orienteering, wilderness survival, wildlife viewing, and kids & family programs. All of the programs are free, so get out there and enjoy!
The Fall 2011 Issue of Outdoors in New York City ("the free newspaper of outdoor adventure") is available for download in PDF form at this link. It includes dozens of resources and events at Parks Department locations throughout the 5 boroughs.
The New York City Parks Department is offering an Advanced Canoeing outing this Saturday, July 9, from Noon - 2:00 at Bayswater Park (meet at Bay 32 and Beach Channel Drive).
From the email announcement: