It was the TARDIS. If there's one thing the Doctor has faith in, it's the TARDIS. And if there's one thing he could not be without, it's the TARDIS. Behind the door was some sort of destroyed TARDIS.

Guys, Rory didn't have a door. Which means he didn't have faith in the Doctor, didn't have faith in Amy, didn't have faith in himself. That's heartbreaking.