Dark mysterious underwater scene, Hogwarts castle ruins submerged in murky depths, old stone walls covered in seaweed, dimly lit by glowing jellyfish, a giant squid's tentacles wrapped around a crumbling tower, eerie fog rising from the seafloor, a lone student in a diving helmet, holding a lantern, surrounded by schools of small fish, subtle ripples on the water surface, ominous ambient lighting, cinematic composition, misty atmosphere.