계단이 · 계단을
stairs, steps, staircase
Example
엘리베이터가 고장 나서 계단으로 올라갔어요.
The elevator was broken, so I went up the stairs.
Word parts
계 step+단 level
Literally 'step levels'.
Good to know
In everyday speech it's usually pronounced [게단]; ㅖ after a consonant often sounds like ㅔ.