Those tiny little cute dragons that Daenerys have don't appear to be staying tiny or cute. The dragon cuts a very big shadow. On first viewing I thought it had to be Meereen, the third city in Slaver's Bay and the only one we hadn't seen so far in the series. We of course saw Astapor where the Unsullied came from, and we saw Yunkai at the end of season three. But doesn't match the description of Meereen at all you know, there's a distinct lack of pyramids. From numerous replays of it, I'm 95% certain that it is King's Landing. Which makes it all the more confusing as to what on earth the dragon is doing there. My only guess is that the dragon in question is Drogon the dragon that goes roaming a bit and becomes Daenerys' dragon-steed of choice. But I wouldn't have thought it would be that big yet, in the time period we expect season four to be in. So my personal theory is that although it's a great opening shot, I think this will somehow be featured in some sort of vision by one of the characters in the show a vision of a future that we haven't even reached in the books. Unless of course Drogon takes Daenerys on an extremely long ride to Westeros and then promptly turns around and goes back to the Dothraki Sea to end up where we see Daenerys and her dragon at the end of A Dance With Dragons.