Ah - you're an overseas visitor then!
Here in the UK, street level is called the Ground Floor. Pretty neat, since it's on the ground...
Yes, I know YOU know that too. But wait ...
Then it goes pear-shaped...
In England, the First Floor is the one that is up one flight of stairs, so OK, I concede it, you're right, it's not REALLY the first floor.
The floor they built first is the ground floor. I know. I can see that.
But anyway, that's how it is, here in Great Britain ...
(There's another helpful window like this when you get to the First Floor - I expect you can hardly wait)