廊下

How it works

This is the “there is X in a place” pattern. The location 廊下(ろうか) (hallway) comes first, marked by に (in) to set the scene, then 箱(はこ) (box) is pointed out as the subject by が (subject). The verb ある (there is) is used for inanimate things — a box can't move on its own, so it gets ある (there is) rather than いる (there is (living)).