"You will go to the heart of the TARDIS. You will see more of the TARDIS more properly than you’ve ever seen it before."
- Steven Moffat, Head-writer
As a fan of the wondrous time-space machine called the 'Time And Relative Dimension In Space' or TARDIS, I can't wait for the episode named "Journey to the Centre of the TARDIS" (7x11).
The very first Doctor Who episode I watched, "The Eleventh Hour" (5x01), had Matt Smith's Doctor clambering out of the TARDIS claiming to have fallen in the swimming pool in the library of the TARDIS. Ever since then, I have been very curious about this "bigger on the inside" police-box.
Also, one of the best new Who episodes that I have seen, "The Doctor's Wife" (6x04), had the TARDIS being a woman who is called "Sexy" (obviously)-
"She's a woman and she's the TARDIS."
The Doctor's longest companion has been his TARDIS, and I think it will be very interesting to see some of its interiors properly, even though we won't be seeing the Doctor's bedroom :(