In the game "Collapse Sky Railway", "Rear Window" is a special achievement task that requires players to perform a series of operations in a specific scene in the game - the Daydream Hotel - the real area to achieve it. The specific steps are as follows:
Answer: We need to investigate all the rooms in the Daydream Hotel real-life map to unlock the achievement.
1. First, we enter the game and select the Pinoconi map.
2. Then we came to the Daydream Hotel-the real 2nd floor location.
3. We choose any teleportation point and then move towards the hotel lobby.
4. Afterwards, investigate the corner of the hotel to obtain all the room cards for the rooms on the second floor.
5. Go to the room and investigate to complete the [Rear Window] achievement.
The above is all about how to achieve the back window achievement in "Honkai Impact: Star Rail". For more game guides, please click on the source code website.