I got home mid-afternoon, and since I live on the first floor (second floor to you USAians)...
So I curious... do they call the first floor the basement? Or like Ground Zero or something?
Ground floor. Actually in some houses where the main living area is up a few steps, but the area below is not considered a basement, you have (say) four stories called "lower ground floor", "upper ground floor", "first floor", "second floor". In the same way, the building I work in has four stories, labelled -1, 0, 1, 2; the main entrance is on 0, but there are other entrances on -1.
The hospital next to my home was extended recently - down the hill; as a result, the extension has six stories labelled -4, -3, -2, -1, 0, 1, with the main entrance on -4.