ground floor 
noun British
The floor of a building at ground level: [as modifier]: a ground-floor flat...
- It was a ground-floor flat in one of the redbrick two-storey buildings that made up one side of Ormond Square.
- Opposite this is an anonymous-looking office building with a large ground-floor window.
- He said the attacker left by a taxi, only to return later on foot and smash a ground-floor window to the building.
Phrases
get in on the ground floor