bottom floor; lowest floor
Refers to the lowest floor of a building, typically the ground floor or basement level.
The bottom floor of this building is a parking lot.
Please take the elevator down to the lowest floor.
Compound of 最 (sai, 'most') + 下 (ka, 'lower') + 階 (kai, 'floor'). The reading さいかかい follows standard on'yomi.