Concerning the question "2. Is there any explanation behind the effect?":
Look at the following figure:
Locally, in other words: when you look only at a sectorial part of the figure, you see a staircase, and there is no visual paradox (other than that it is not clear whether going clockwise goes up or down, but that is another matter). It is only when you look at the figure as a whole that the idea of a staircase is no longer sustainable.
The main cause of the illusion is the fact that our brain is automatically interpreting the two-dimensional input of a part of this figure as an image of a scene which is in reality three-dimensional.
Note that in the case of a real three-dimensional staircase even our two eyes looking at it would not be able to resolve the front-back ambiguity alluded to in the sentence in parentheses above.