입구를

입구를

"입구를" means "entrance" (object marker included).

In this sentence, 입구를 is the object of the verb '유지합시다', meaning 'to maintain or keep'.

도서관의 입구를 깨끗하게 유지합시다.

Let's keep the library entrance clean.

입구를 is used as the object of the verb '지나면', meaning 'to pass through'.

입구를 지나면 새로운 광장이 나타납니다.

After passing through the entrance, a new plaza appears.

Here, 입구를 is the object of the verb '찾지 못했습니다', meaning 'could not find'.

출구가 보였지만 입구를 찾지 못했습니다.

I saw the exit but could not find the entrance.