Is the cat going up or down the stairs?

Down

Down.

You're right about the edges of the stairs Elegran!

Changed my mind again...

Down - edges of steps protrude, which would trip you if it was the other way. The light at the top is confusing, it makes it look as though the cat has left the street and is climbing up a flight of internal steps.

I would go with one of the comments below the article - it is Schrodingers cat, it is going up and down at the same time.

I thought up.

Of course, it could be down but I'll stick with up!