I went inside back in September when the National Trust had that open day - it was amazing, walked around the camera runs first, then into the bedroom, garden & main house where Big Brother called you to the diary room (for your photo in the chair) & finally into the task rooms where they had laid out all props & costumes used over the series. They even got ex housemate Jackie Travers in the house to mingle. There were no real limits & we were free to roam around everywhere, pressing the BB bell for the diary room, up in the hut, I even sat on the bedroom loo! lol.
Then they took us to the reality gallery where they monitor all the cameras & we saw the box where Big Brother talks - she (big bro) was in there & came out to give a long talk on how the show is put together, and then we got ten minutes free run in the BBBOTS studio
It's a lot smaller than expected, but cozy none the less.