This rugged woodland preserve at the top of the Palisades cliffs is administered by the Palisades Nature Association. Of the total 165 acres, 120 acres lie within Tenafly's borders. The preserve offers magnificent river views, waterfalls, many species of plants and animals, and 235 listed species of birds. Since it is a sanctuary rather than a park, Greenbrook restricts walking to marked paths. There is an annual membership fee.