玄関 and 廊下: entrance areas and corridors
Distinguish an entrance area from a passage between rooms.
At the entrance
玄関 (げんかん) means an entrance area. 「玄関に靴を置きました」 means leaving shoes at the entrance.
「玄関で客を迎えました」 says guests were welcomed at the entrance. で marks where the action occurred.
A passage between rooms
廊下 (ろうか) means corridor. 「廊下を歩きました」 describes walking along a corridor, with を marking the route.
「廊下の奥に部屋があります」 locates a room farther down the corridor. Interpret 奥 relative to the viewpoint in context.
Location versus route
「玄関から廊下に入りました」 describes moving from the entrance into the corridor. Separate the origin from the destination.
「廊下に荷物を置かないでください」 asks people not to leave luggage in the corridor. It does not report that luggage is already there.
Does を in 「廊下を歩きました」 make the corridor an object being changed?
Show the answer and why
No. Here it marks the route walked along, not something altered by the action.