noun
second basement level; subbasement
Refers to the second floor below ground level in a building, often labeled B2 or BF2.
駐車場は地下二階にあります。
The parking lot is on the second basement level.
エレベーターで地下二階まで降りてください。
Please take the elevator down to the second basement floor.
Compound of 地下 (underground) + 二 (two) + 階 (floor).