The locks I am most impressed with are from the days of alcohol prohibition. Some doors to speak-easy's looked like part of the wall, had no key holes. Rather just small holes all over the "wall" and you had to poke a piece of metal through the right holes and push/pull the wall in a known way. No windows, no appearance of a room, just a wall. The stairs leading down to it would usually go right past the "door" into a basement storage room with nothing exciting to see. The cops could walk right past the door a thousand times. It might be fun to build a home like this. I suppose you just have to design it so people can not see where you actually entered.