The old concrete slab that you see was previously used to mount six inch guns used for the defense of the Boston Harbor in WWII.
The grown over mound with a visible blast door behind the bus was the camouflaged bunker that housed troops, supplies and ammunition. Note that I had to pull exaggeratedly close to the front of the site to get my rear wheels up high enough that the leveling system could handle it.
The old reinforced concrete observation tower still stands. The first federal use of the property was in 1880 when it became a life-saving station. After WWI it became a Navy radio-navigation station. During WWII it was a potent Coast Artillery site. It became an Air Force Field Station in 1948. At that point it became an antenna range for the noteworthy MIT/Harvard Radiation Laboratory (the famous "Rad Lab"). Shortly thereafter it sprouted the huge ELF (Extremely Low Frequency) test antennas which verified the capability to have limited communications with submerged submarines a half a world away.
In recent years the historic little hilltop has hosted many thousands of military families as a vacation site and recreation area. We'll be here until the 15th. I haven't gotten up early enough to capture a sunrise, but looking shore ward there are some nice sunsets.