On a totally unrelated note, I have been rewatching Season One of A:TLA, and I just watched the Winter Solstice two-parter. This is the episode where Aang first enters the Spirit World and meets Roku. An interesting thing I observed that I never noticed the first time around is that when Aang enters the Spirit World, he meets up with Roku's dragon. The dragon and Aang fly to Roku's Island, but on the way they fly over General Iroh and a bunch of Earthbenders. Iroh sees them! They're in the Spirit World; nobody should see them, but Iroh does.
It's a story thread I feel must have later been dropped, but I wonder what the original intention of that was.
It wasn't dropped, as you'll see when you get to "The Firebending Masters" in Book Three.