I worked on the AC units upstairs at Graceland back in 2003. It was September and it was HOT but they wanted to wait until after the Labor Day weekend to send us in. I was just a kid making hourly pay and from what I remember they had us all sign a form and we were escorted upstairs by at least two people with keys. But I don't think there was a crazy double-lock door or anything, it just was two doors had different keys from what I recall.
My job was to watch the temperatures, literally. So I was stationed in what looked like an old office towards the "back" of the house and had to program several of those old rotary-style timers for AC and refrigeration units. It usually was someone with a walky-talky reading me temps and me confirming that the pins were set to the correct time configurations. We'd get called when someone noticed an AC unit either running all the time or not running at all, and usually those pins got messed up.
So this was just another one of those jobs, plus changing filters and any other things that needed maintenance.
I was the youngest guy on the team, so I really wasn't allowed to do much, though the guys would occasionally tease me on the walkie and they def did that a lot on that day. I did get nosy and look in one of the banker's boxes that were stacked in the office and it looked like pretty boring paperwork, so that was that.
So, I can say that I've been upstairs. We went up the back staircase, fwiw. And I do remember every door getting closed as it was entered, and probably locked, which is why we had walkie talkies.
The carpet was old, so I do remember thinking, "Wow, this was probably here when Elvis lived here". It smelled like an old office, paper and a little bit musty.