The writer revealed that the instalment will contain "great visuals" and that new sets have been built especially for the episode, Radio Times reports.
"We've built the rest of the TARDIS!" Moffat enthused.
He continued: "The idea is in the title; we're going to journey to the centre of the TARDIS. We've got some great visuals for that."
Ashley Walters, who guests star in the episode, added: "In our episode it'll be the first time people get to see so much of the TARDIS."
The upcoming series of the BBC show will feature classic series villains the Ice Warriors as well as the Cybermen.
Jenna-Louise Coleman stars as the Doctor's new companion Clara. She appeared in last year's Christmas special but fans were left with questions over her identity.
Moffat recently revealed that former show boss Russell T Davies has turned down the opportunity to pen a new episode of the show multiple times.
Doctor Who returns with the remaining eight episodes of series seven on March 30 on BBC One.
Watch the trailer for the series below: