Girl looks into mirror, sees demon swimming towards her [closed]

I remember watching parts of a movie on tv some years ago. I missed the beginning, and saw some parts from the middle and the end. I didn't really understand what was happening, but I can provide some details about what I remember (including the ending, so stop reading if you want to avoid spoilers):

• the movie had a very creepy atmosphere, and the image seemed to be quite desaturated if not black and white
• a guy was having some weird dreams (or visions?), including an ominous figure walking behind some pillars; the dreams always stopped before he could see who it was
• there were some messed up mirrors in a building, showing and/or doing horrible things (I think including killing people); apparently there was another world behind them, with a demon or several demons
• a demon was trying to come out into the real world, and several characters were trying to stop it
• the part I remember most clearly: in one scene, a girl went to a mirror and the demon was kinda swimming towards her from the other side; they joined hands, then the girl went into the mirror, somehow pushing the demon away; then I think the guy (who was in the room) smashed the mirror; I understood this as a self-sacrifice of the girl
• and the really creepy ending: the guy is having that weird dream again, and now he can see the figure - it's the girl from the previous scene

Some details may not be accurate, but that's how I remember them. I found "Into the Mirror" (2003) and "Mirrors" (2008) on wikipedia, but I can't find a description of the ending that matches what I remember. And I think I saw (those parts of) the movie before 2003.