Dr. John Watson : [about Sherlock's "mind palace"] It's a memory technique. A sort of mental map. You plot a-a-a map with a location. It doesn't have to be a real place. And then you deposit memories there. That, theoretically, you can never forget anything. All you have to do is find your way back to it.
Dr. Stapleton : So this imaginary location could be anything. A house or a street?
Dr. John Watson : Yeah.
Dr. Stapleton : But, he said palace. He said it was a palace.
Dr. John Watson : Yeah, well, he would, wouldn't he?