What is the name of this song?

The song has a slow beat and it's the same for the whole song. There is also a slow melodic acoustic guitar playing with a woman singing softly. The song has also featured on some adverts, I think most notably on an Assassins Creed advert (Not Assassins Creed Revelations one just in case). I know it not that much info, but can you just name all the songs that come to head from this description. I really need to find the name of this song.