@Le_newtype, it's about an old serial killer reminiscing about his past. As Lucas put it, the song is: "a lyrical story about an old man who is hallucinating in a sunny park. He is unsettled by visions of various atrocities he had performed, at that very park, in his younger days".
I looked at the lyrics to the song and I can't figure out what's going on in them. Is this song about dead women and animals all over a field as the narrator becomes more and more drug-induced? http://www.lyricstime.com/cinema-strange-greensward-grey-lyrics.html