Merlin waits a couple of days after Arthur's coronation to approach him about it. There was just too much going on in the hours immediately following the ceremony, and too many nobles demanding Arthur's time. In their stolen moments alone, talking wasn't anywhere on Merlin's list of priorities.
Once all the guests have retired back to their own estates, Merlin finds his moment, knocks on the door and enters Arthur's chambers without waiting for an answer. The new king looks up, weary, but his eyes brighten when he sees Merlin, and it makes Merlin feel warm inside in a way that nothing else has ever done.
"Merlin. You know you don't need to knock." His voice is rebuke and affection, now weighted heavily toward the latter; a common combination to Merlin's ears. He smiles, but he approaches Arthur's chair with an uncommon seriousness, and Arthur sits up a bit straighter when he notices.
"What is it?"
Merlin bites his lip—Arthur's eyes darken, but it's not the time for that. Merlin's made up his mind to do this, and he's not going back on it.
"I… have a favour to ask."
Arthur doesn't miss a beat. "Anything," he says, and Merlin knows he means it. But he doesn't know what Merlin is asking for, and he won't be entirely surprised—disappointed, but not surprised—if Arthur changes his mind when he finds out.
"I have this friend, and… and your fa—Uther. Uther had him locked up. He's been locked up for a long time. I know it's a lot to ask—"
Arthur's got a funny look on his face. "Merlin, you know there's no one left in the dungeons. Your friend was pardoned along with all the other prisoners when I was crowned."
Merlin just gazes at him, sadly, through lowered lashes. It's a dirty trick, but…
"He's not locked up in the dungeons. It's— The thing is, he's locked up… below the dungeons."
To say that Arthur had been surprised by Merlin's request would be an understatement. That Merlin was the most powerful sorcerer he was likely to meet? Wasn't so hard to believe, considering everything Arthur had seen—and survived—since their first meeting. But that he was on friendly terms with the last dragon in all of Albion… well, that was Merlin for you, he supposed. After all, he was on… friendly… terms with the King of Camelot, too.
Once he'd gotten over that, though, his only real concern was whether the Dragon, if released, was likely to seek revenge for his imprisonment in some thoroughly unpleasant way. Like, for instance, burning Camelot to the ground. Or, say, eating Arthur.
Merlin had just snorted at that. "Of course he won't." He quipped, briefly pausing his tongue's exploration of Arthur's stomach to do so. "That's my responsibility." Then he grinned and bit down lightly, and Arthur had stopped worrying about the dragon for a while.
They hold a huge festival in Camelot the day that the Great Dragon is released from his cave.
It had taken a while, and been more complicated than anyone had anticipated, but Arthur is glad he did it. The Dragon had been… well, apparently genuinely happy when Merlin had first taken him down to the cave. Not that Arthur knew much about dragon emotions, but as terrifyingly pointy as the Dragon's grin had been—Not going to eat you, Merlin had whispered at his shoulder—it had been a grin nonetheless. He wasn't sure what was more terrifying—a dragon who wanted to eat him, or a dragon who smiled at him.
The oddest thing was that the Dragon had made a special request: to be given a way out of the cave, but with permission for him to come back when he liked. Arthur didn't mind granting it, though he wondered why the Dragon would bother. If Arthur had been locked up in a cave for that long, he wouldn't ever want to see the inside of it again.
It's not until late that night, when Merlin appears out of nowhere saying, "You have to see this!" in a half-awed, half-scandalized voice, that he finds the answer.
Climbing up the wall of the cave isn't very hard, which Arthur hadn't expected. But then, apparently Merlin had managed to do it on his own (and they were going to have a talk about climbing around over truly dizzying chasms without telling Arthur), so it really couldn't be overly difficult.
Arthur doesn't have a problem getting to the upper ledge. It's when he gets there that he nearly falls off the edge.
Or, Camelot as it would look if it came up no higher than Arthur's waist, its buildings were missing large chunks of their walls, and it was populated by strange little dolls…
Dolls that are dressed rather suspiciously like himself and Merlin, actually. And a few others… he recognized Gaius, and Morgana and Gwen. And that could be Lancelot, off to one side. He doesn't see his late father anywhere, but there seem to be other portions of this strange landscape; perhaps Uther's doll is in one of those. That oddly looming cave, maybe. Why there is a cave carved into a cave is a question that makes Arthur's brain hurt.
"They're pretty cute, don't you think?" Merlin had picked up his own doll, which was a foot tall and seemed to be made of stone but, as Merlin aptly demonstrated by waving the doll's arm at Arthur, moved like no stone he had ever seen. "He must have been bored."
Arthur takes a moment to look over the stone city again—the Great Hall in the castle, Gaius and Merlin's rooms, Arthur's stable…Arthur's bedroom…
"There's bored," he drawls at Merlin, "and there's insane. This," he gestures broadly, "is insane. No wonder you're so strange. You've had terrible influences."
Merlin laughs at him, setting his doll-self down next to the Arthur doll and perching his real self on the sloped roof of one of the castle's towers. Arthur grabs his hips and slides him around until Arthur fits comfortably between his knees.
"I mean it. I don't want you associating with any more dragons," He orders in his most serious voice. Merlin is, as usual, not impressed, and Arthur falls just a little bit more in love with him when he leans forward and sticks his tongue in Arthur's ear.
"Except a Pendragon, of course." The warm air of Merlin's breath sends a shiver up his spine, and he smiles into Merlin's hair.
"Well, obviously," he retorts, and they're back to not-talking again.