It's very hard to find information about this campground which is closed for 2020. When open, it's for walk-in only and you need to check in with Erving State Forest (about 15 miles away) first, but there is a phone number to contact them. The entrance road is marked with signs, but I accidentally drove past it the first time, but Google Maps took me directly to it. It's a long curvy road that ends with a small parking lot at a T junction. In Nov 2020 the road to the left is closed because a bridge is out; the road to the right leads to the campground and Gate 36. This was gated in Nov 2020 as the campground was closed due to Covid-19, so I'm not sure if they'll open it in the spring.
Some of the sites are definitely walk-in, with a narrow trail leading from the road. It's possible to park at other sites; I'm guessing the gate at the beginning of the road toward the campground is open when the campground is open. If so, high clearance vehicle is definitely preferred. There's no map on the website and the one I found online elsewhere was outdated/incorrect and the one painted on a campground board could be clearer. I didn't find all of the campsites. Bring your own water. There is a composting toilet located near the group site in the field.
If you continue past site 15, you'll head through Gate 36 out toward Soapstone Hill which offers a great view of Quabbin Reservoir and sunsets.
This website provides some general information about hikes and exploration in the area that surrounds the Quabbin Reservoir. https://quabbinvalley.wordpress.com/ You'll find cellar holes throughout, remnants of the towns lost in the 30s to create the reservoir.
Cell phone coverage is faint to nonexistent on Verizon. You may want to download offline maps before you head out here. If you're into geocaching, download those, too. There are several along the entrance rd and in teh area.