Ambience defines this library. It's full of eerie soundscapes that can instantly bring vibe to any kind of thriller / mystery / horror game. 10/10
As an amateur sound guy I own a plugin called Mysteria for Kontakt, it's $300 and is basically an 'eerie sounds' plugin with eerie vocals as well.
This is less than 10% of the price, lacks the vocals, but evokes that unnerving feeling just as well, which makes this a no brainer. Highly recommend!