The Doctor: This painting doesn't belong here - not in this time or place.
Clara Oswald: Obviously.
The Doctor: It's the fall of Arcadia, Gallifrey's second city.
Clara Oswald: But how is it doing that? How is that possible? [She walks up to the painting and puts a hand out to touch it.] It's an oil painting...in 3D.
The Doctor: Time Lord art. Bigger on the inside. A slice of real time... frozen.
Screencapped from Doctor Who's 50th Anniversary Episode 'The Day Of The Doctor'