B1
the floor of a building that is at the same level as the ground outside
Dictionary examples:
On the first floor, you'll find our 'Guess the Smell' challenge room. (0.0)
Our pet elephant lives on the first floor because he can't use stairs. (0.0)
The first floor is where we train our team of professional pillow fighters. (0.0)
She works on the first floor. (8.8)