In my story there is a hill and the hill looks like a stair case with three steps what would you even call each step? (Without saying “step” because that’s not right for the moment he is in).
In the far east and on the Mediterranean we describe the "steps" on mountains used for agriculture as Terraces. If you do a google image search for 'mountain terrace', you will see hundreds of "stepped" mountains - https://www.google.co.uk/search?q=terraces+mountain&tbm=isch&tbo=u&source=univ&sa=X&ved=2ahUKEwjsxvjF1OrdAhWNRMAKHQo_ARIQ7Al6BAgCEA0&biw=1280&bih=651 was that what you had in mind?
Even though you know something isn't what you describe, using descriptive terminology is fine. Especially if something else follows:
The hill looks like a staircase with three steps. But it can't be an actual staircase, and they can't be actual steps. Instead . . .
The use of looks like is a qualifier, such as seems to be or reminds me of. Whatever follows doesn't necessarily reflect what it is in fact.
Unless of course, your problem is not with the analogy but with the use of the word step itself. If your narrative prevents the use of that word for whatever reason, then you will need to come up with something different:
It's a strange hill. It looks like something purposely built to be walked up, rather than something formed by nature . . .
In clarification from a comment, "it looks like three gigantic steps."
They look like steps made for a giant.
After such a description, you could simply refer to them as giant steps.
You could describe it as a series of interlocking stelae, a path carved by the giants of yore in the bones of earth. You could call them mesas in miniature.
I wouldn’t call it a staircase or allude to it as such. I might suggest describing the climb.
Frer was almost home, but while the distance was not great the ascent was not easy. Carrying the water he slowly climbed the first ascent, seventy feet of rough terrain and sudden level areas. He believed his grandfather’s stories about giants, who else could have moved these massive stones, now overgrown and one with the landscape. Resting briefly, he strode the length of the gentle incline that looked level from afar. The next slope was steeper still, but thankfully not quite as high as the first. Too close to home now to rest, he dug deep and climbed the final slope and saw his father waiting at the door of the hut they called home.