You will find the ruins atop Heyerdahl Hill deep within an area known as Buck's Hollow. At 241 feet, Heyerdahl Hill is one of the highest points on the eastern coast. If you live in the City of New York but are not from Staten Island, I strongly recommend taking the time to visit this site. You quite simply will not believe you are still in the city.
The hilltop was named for the Heyerdahl Family who settled here in Colonial times attempting to grow a grape orchard, which, due to the serpentine rock underneath the soil, was doomed from the beginning. At one point, not too long ago, the ruins of Heyerdahl was the most remote place in New York City. Today while traveling out to Heyerdahl, one cannot escape the feeling of isolation.
Ghost stories featuring Heyerdahl family members are still popular with local storytellers. One tells of the ghostly apparition of a young girl riding a pale horse across the wooded hilltop. During the Revolutionary War fighting broke out between the British and Colonials in what is now called Historic Richmondtown. The girl, fleeing the fighting, rode off into the woods and was never seen again.
There are several routes you can take to reach the Heyerdahl ruins. Certainly the Greenbelt Visitor Center (N40.35.194, W74.08.197) is a good launch point. My favorite starting point is the small parking lot at the entrance of High Rock Park (N40.35.560, W74.07.278).
Please be extremely careful crossing the roadways along the trail. Small children must not travel unsupervised.
From High Rock Park: Pick up a trail map from the events bulletin board inside just inside the park. Follow the Green trail to the Yellow trail. Take the Yellow trail to the Red/White junction. Then follow either the Red or White trails to Heyerdahl Hill. (Red is a gradual climb, while White is pretty steep near the end.)
From the Greenbelt Visitor Center: Take the GVC North "N" trail to the Blue trail. Turn left and follow the Blue trail to the Red trail. Turn right and begin ascending Heyerdahl Hill.
Walk the trails all the way, no bushwhacking required. Once you're close enough, your GPS unit will lead you to the cache. Cool prizes for the first 6 to find.