Pass the Research Facility without killing a Blind One on the DEAD CITY level.

After exiting the underground area of the Dead City you will be on the surface and need to navigate your way through some ruined buildings. Within these buildings there will be giant animals that resemble Apes that will attack you if you make too much noise. These can be snuck past simply enough as they, as per their names, cannot see. You must not harm any of them in any way while playing this section of the level. There are around five or six throughout the level and mostly can be avoided with ease, however the final three you find are all within the same small room that you must find your way out of by activating an electrical panel.

If you're playing on easy you can simply sprint through the level and just tank through any damage dealt to you. You can be spotted as much as you want, you just can't hurt or kill any of the Blind Ones.

The first Blind One that you find will drag you off a ladder via a cinematic. You must either run past this when you gain control or try to sneak away. DO NOT attempt to fight it or you will void this achievement.