This old military base is now part of Gateway National Recreation Area. It may technically be part of the National Park Service, but it’s still basically an abandoned military base. There’s Battery Harris, which is semi maintained, and there are plenty more buildings that have been left to go back to nature. This park doesn’t have much in the way of amenities, but there are plenty of ways to get yourself killed.
There are some sports fields, a theatre, and some art galleries. Bathrooms are few. Swimming and exploring are technically verboten, but there appears to be no enforcement. As always, your mileage may vary. Don’t get yourself killed, arrested, or covered in poison ivy.
Head a little bit east and you’ll find yourself at Jacob Riis Park. Breezy Point is to the west, once you walk past all the houses. It feels like you’re on a different planet from New York, even if it’s there to protect the city.