If the White House is the castle, maybe green castle is Camp David?
Also, does anyone remember a couple of months ago, late one night, there were reports of many submarine detecting planes flying in that area north of Seattle. It was right around the time when when there were some threats. I think there were some posts that showed tracking images of the planes.
Camp David: good guess indeed
True, Green Castle could well be Camp David, per Lady Jane.
I recently saw one of those old crumbs about GREEN CASTLE/RED CASTLE and IIRC, a presidential residence would fit. Must look back.