As a sidequest (and requirement for the Golden Ending), you can collect furniture. How is this implemented? You go into a particular room, Juste comments on how boring the room looks, and decorates it with the furniture he's collected. He's decorating a room in the castle because he can.
Upon beating the Hard Boss Rush with Simon Belmont, you're treated to a clip of the original Castlevania "castle-destroying scene", and the words "SIMON BELMONT FOREVER" appear over the image.