You're a Mile Away and You Have Their Shoes by Mad Maudlin Arthur wanted to know what was going on in Merlin's head. He just didn't mean it so literally. A very intriguing role reversal seen through Arthur's confused pov with both Merlin and Arthur remaining very in character plus lovely interactions with all the main characters, including the dragon. Also, as someone notes in the comments on LJ, possibly the only fic that has Arthur finding out about Merlin's magic AND Merlin finding out about Arthur's magic. Highly enjoyable.