@Weird TalesWe got to stop for doughnuts and take many bathroom breaks along the way.
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The prisons of the Demons are before the Angels Chamber, I believe.
It's a long hallway connected to a stairwell that leads up to a castle, which is also a prison for human criminals.
However, I would think the demon's individual prison cells are probably all unique and different, meaning they might be lower, deeper, or something else entirely. I'm unsure, but they could very well have to climb another floor.
But yes, Eyra's own castle is at least 30km away as stated in the first post.