This is a mix of land owned by the BSA and managed by the Daniel Webster Council and conservation easements or fee ownership by the Lakes Region Trust or the State of NH. The Griswold Boy Scout camp maintains the access roads and most of the trails up onto the ridge line. The property is open but there is no overnight parking or camping. When scouting activities are in session you need to be particularly respectful of that activity
Getting Started
There are two major entry points into the reservation Griswold Road (Hidden Valley Camp) and Manning Lake Road (Camp Bell). There is limited parking when scouting activities are going on but off season weekdays and during the winter there's plenty of room. There are no facilities or services for non-scouts. No trash and no toilets.
My preference, having used both sites is to park and hike from Camp Bell. It keeps you out of the center of the scouting activities and allows you to access the Mount Mack and Mount Klem areas from which you can go East or West on the ridgeline. To access Mount Anna or Straightback it's actually easier to use the trailhead off the end of the Alton Mountain Road.
When to Go
This site is only accessible during daylight hours and is patrolled by rangers working for the Scout camp. Avoid Hidden Valley during the summer and on spring and fall weekends. Avoid Camp Bell about the same though there is parking for a few cars near the Manning Lake boat launch and a short walk in the access road.
On leash in most areas during scouting activities as you could meet scouts at any time. Off season probably similar to any conservation property. Be a responsible owner!