One word. No further elaboration. None could be given that would make it sound any better than it was.
Niflheim was a misty, cold place. There were perks to Hel being there, and he doubted even she had discovered that yet. It was where the world began, and it was dark and mysterious. And probably not a fitting place for a young woman. Odin knew all this. It was why he chose it.
None would dare venture there. And with a little luck, she might actually find it comfortable enough to prevent her from actually become the child of the prophecy. Which was really what it all came down to. Sometimes, every now and then, Odin wished he'd never visited that damnable Volva. Sometimes. But his thirst for wisdom was to great, and even greater was his sense of self-preservation.