Everyone knows about the facility including Russia.
It was on History Channel about 15 years ago.
When I was an ROTC cadet at Gettysburg College in the late 80s much of our support came from Ft. Ritchie, MD. Site R was one of the worst kept secrets even back then in the midst of the cold war. The huge antenna array sticking out of the mountain top was pretty obvious. Likewise, in the winter, when most of the mountainside was covered by snow, there were some patches where snow wouldn’t accumulate, kind of like a heated driveway.