Riverview Hospital, a large mental health facility used as the main set in season one, episode ten, "Asylum", has also substituted for a prison, a regular hospital, and an apartment building on different episodes of the series. This is evidenced by seeing the same distinctive staircase in different episodes.
Dean, there's ten times as much lore about angels as there is about anything else we've ever hunted.
Dean Winchester: You know what, there's a ton of lore on unicorns too. In fact, I hear that they ride on silver moonbeams, and that they shoot rainbows out of their ...
In several episodes, characters mention the book of Revelations, from the Bible. However, it's just Revelation.
The opening credits are shown during an early scene.