As I said, an easy one. Your turn to set the next exercise.
May the respective Christian and Norse gods bless you, sir. (It so happens -- which helped -- that some four years ago, I set a question here, answer being that station; with a very similar clue.)
Close by, but not in, the county of witches: request or order (concerning watercourse) to one such, who transmogrifies different elements / substances.