It is wind :3
What is gentle and violent at the same time (Around the world, wind is blowing violently or gently), what is always howling but also whispering (The wind is loud and violent somewhere, but also silent and calm in some other place), who crushes castles and strokes the rubble (The storm and wind destroys the castle, and the gentle breeze after the storm strokes the remains), What is everywhere and nowhere? (Wind is everywhere, but is also invisible, so it seems like it is nowhere)
*Bows*