Hello there,
I'm almost done with the game. Now I have to "charge" up my crystal which I believe is nearly impossible to do without a guide. The problem is, how do I get back to the "fantasy world" in China with the flying dragon? I have already completed it and now none of the NPCs wants to talk to me anymore. The entry in the turtle room is locked and I can't progress any further. Have I screwed up my playthrough?
BR
Finalzero

Greetings,
I've done the quest in China once but can't recall most of the details so I'm trying to answer your question by this walkthrough.
If I understand correctly, you left the house of the Dragon without charging the crystal at the golden doors between the low-able bridge and the dragon-boat in the fantasy world. And from what I remember once you opened the entrance to the house through the guidance from Wu Tao-shih, you can open it anytime later even it was closed after leaving the room of the turtle. Just click on where it was and the red wall will fold again as before.