A large frozen fortress built on a ...

A large frozen fortress built on a snowy mountain. The structure is made of packed ice, blue ice, stone bricks, and spruce wood. The building has four floors connected by staircases and long hallways. Each floor contains multiple separate rooms with different sizes, including small guard rooms, larger halls, and hidden side chambers. The entrance has a tall icy gate and two frozen towers on each side. The second floor has narrow corridors and prison-like rooms. The third floor contains a large throne hall with pillars. The top floor is a circular room with a broken icy ceiling. Add frozen details, cracked ice, hanging icicles, and snow layers for atmosphere.