Castles
Well it does have a castle atmosphere and tone to it which kind of builds up the setting even further. You walk around as a ninja knight who guards the princess/prince from outside harm and enemies. You soon begin working for a darker lord... maybe Ganondorf?
The bass line and drums seem to work together to create a very dark area feel here as they make the person feel most likely unwelcome at the castle lest they be a knight themself with a message for the king. The ambient trumpet and piano notes add even more to the dark atmosphere.
Overall, nice castle theme, would work well in a dark castle like level in a game.