In this scene, Father Miller, who's attempting to rid the 12-year-old Regan of the demon, falls from Regan's window down these narrow steps to his death. According to Culture Trip, the stuntman assigned this task had to fall down the stairs twice to perfect the scene.
I found the stairs a couple weeks ago after walking past them earlier in my rush to get to class. But once a classmate told me where they were, I made a point to walk them the next week.
I'm happy to say that I did not fall. But I did huff and puff a little. And I definitely felt a sinister vibe. The stairs are steep and creepy, just as billed, and apparently, if you try to count them, you'll never come up with the same number twice.