This is a simple, enjoyable optical illusion. Just stare at the picture for awhile, and at first you’ll think that the stairs go up. A fairly simple illusion. But as your eyes look around the picture, and especially if they glance to the left corner, it helps your brain think of the stairs in a different way.
They start to flip perspective and it looks like you’re looking UP at the stairs instead. Then your brain will flip it back. It appears to be impossible to imagine the stairs going both ways at the same time. The picture doesn’t flip the picture, it’s how your brain interprets it.
As you look around the image, waiting for it to flip, I’ve found that looking at the second peak from the left seems to work well. For some reason – in the author’s mind at least – that leftmost staircase looks like it is already upside down. So then as I shift my gaze to the other stairs, they too seem to be upside down for a moment, and then usually they shift back again!