The Dragon's Palace was an area in Plants vs. Zombies: Journey to the West and later in Plants vs. Zombies: Great Wall Edition, and is the final area exclusive to the former's Adventure Mode. This area took place in the same location as Underwater World. In an underwater palace, presumably in the East Sea.
This area functioned exactly the same as Underwater World. Sun fell from the sky in a serpentine pattern, and plants required Oxygen Algae in order to say planted.