Patching and Plastering - bathroom wall has ripples

I want to repaint my bathroom one wall has ripples in it that you can feel. I asked previous owner and he doesn't know. Could someone help me?

Is this a drywall wall?

Drywall could have been put up backward. Really.
Could have been a defective sheet.
Could be moisture related paper is delaminating
Could be a poor finishing job.

Do a little measuring and figuring. Is it at the elevation where there is likely a joint?

Is moisture a problem in the bathroom? Does the wall get wet? Do you get the humidity out of the room?

Has it always been that way?

Are the ripples in an angle?

How wide is the frequency of the ripples?
How high is the amplitude of the ripples?

How large an area is effected?

Are the walls smooth?

Under any lighting conditions can you see the ripples or only feel them?

Yes -describe this better. And of all the bathroom walls, describe what is on every bathroom wall, and which one this wall is, and if it is on the entire wall or part of it, and describe it better, and/or show us a picture.