Stayed 3 nights at the Campground, which is at less crowded Western part of the Park. Tent/trailer sites. Bathrooms with showers. There is a campstore with the basics- food, ice, firewood, but no beer. The Eastern end of the Park (about ten miles from the campground) is the attraction, with the three Falls, and it can get crowded. The trail system is okay, but not challenging as the terrain is mostly flat. If coming from a distance, book a night each at the Campgrounds here and Watkins Glen. Make your reservations in advance.
I have spent dozens of nights in Harriman, mostly 4 day/ 3 night loops. Pure backcountry an hour North of Manhattan. Carry in/ carry out. Bring water purification. Water is abundant in cooler months, but expect to purify lake water in Summer. Camp in or around shelters. Hang you food or carry a bear canister; black bears do inhabit Harriman/ Bear Mountain. Pick up NY NJ trail Conference Map set #118-119. Carry/apply insect repellant to repel deer ticks that carry Lyme disease.
Love this place. Have gone the last three years, and I have reserved again for August 2018. You'll need a boat or canoe (rentals available in Saranac Lake). Sites have tables, fire rings, and outhouses. You'll need a tent, bag, pad, cooking equipment, etc. Bring warm clothing for nights; temps can drop 30 degrees in hours. Sites are carry in/carry out.