The second sentence widens the point of view to show Harry and Hermione in a scene. If we break it into pieces you can see how the sense of scale widens from close to gigantic.
They were standing hand in hand in a snowy lane under a dark blue sky in which the night's first stars were already glimmering feebly.
Snowy, dark, feebly: these aren’t bright, happy, energetic words; they are the little details that make the scene even more spooky
He was looking down into a narrow chute that led into a darkness from which rose only the sound of dripping water and the faint smell of mold.
He was lying fully-clothed on a rusting platform above a dark reservoir in which the city's teeming rats were hunting quietly.
She was propped upright on a pillowy bed in a soft pink room around which the scent of berries and vanilla hung just a little too sweetly.
