There are a total of 7 visions spread across Metro: Last Light, “The Dead City” mission and finding them all would add a lot to the story and you will also get a achievement “Back To The Past” worth 20 Gamerscore or if you are playing on Playstation 3, a bronze trophy.
Metro: Last Light Vision Locations
While playing the game, you will come across areas where you will encounter strange voices echoing. All you have to do is follow those voices and you will get the visions.
These visions usually appear when you go through the spooky areas where humans once used to live and now these areas are abandoned and occupied by the horrors of the past. These visions add quite a lot of richness to the game and it is advised that you find them all!
The game will automatically save the visions you collect and once you have collected them all, you will get the achievement/trophy.
It must be noted that 3 out of 7 visions are miss-able and you must pay heed to them while playing.
Playground – It is unmissable.
Piano – It can be found once you hear a baby crying followed by the sound of a piano playing. Follow that sound upstairs and you will get the vision.
Car Crash – This vision is also unmissable.
Lady In The Shower – This vision can be found near the site of the car crash.
Family Looking Out Window – This vision is also unmissable.
Kid Alone Crying – This vision can be found when you encounter winged mama demon beast up the rooftop.
In The Metro – This vision is also unmissable. And this is the most significant vision of all as it contains the memories of Artyom as a little child.
There you have it! All visions of the Metro: Last Light and 20 Gamerscore.