Told you it was a submarine
So they climb the mountain and as the kids and Mendoza reach the top and try to figure out what the orb in the water is, Sancho and Pedro climbs a lot slower and somehow the crabs are disturbed and are travelling en masse up the side and as our heroes jumps to the orb they are under attack from the pincers of the crabs. Here the 3d animation really enhance the experience since it could pan around the heroes as they fight of the crabs on the orb. Tao and Zia finds a symbol on it and after pushing it and turning some kind of lever they escape into the machine. Mendoza triggers the control panel and as they use the symbol they got from the samurai as a key it activates. The ship sinks to the bottom and as they take control they pass through the water. The music is amazing, the animation fantastic as they do more circles around the submarine and they really got creative with the underwater scene. Fantastic. After travelling some time the machine goes on autopilot into rift and another city of gold, caught in a stone coffin. Zia's medallion triggers it to reveal the true city of gold. They enter an airlock, dismiss the water and can walk around. The statue that signals the docking point looks a bit like the feathered serpent which was an important figure in the original series. Although I can't recall if it was the name people gave Estebans father or if it was some ancient person describing the way to the cities of gold.
The kids active another stage of the city and walk around it, finding water pillars like Morpha in the Legend of Zelda: Ocarina of Time just dangling around. Tao stays behind since he is depressed about Ambrosius betrayal and thinks back to him over and over again, even when it came to the name of the city, which I can't understand what they call it. Sancho and Pedro finds a huge cube of orichalcum (I assume since it is established that Mu and Atlantis used that material due to its conductive properties, and that it is a fantasy element you can do whatever you want with) and as they touch it smaller cubes from it fly around them and they fill their pockets. Zia and Esteban meanwhile finds some crown/tiaras laying around and as Esteban puts one on his head, fooling around a bit, the flying cubes starts to surround him and the episode ends.
I'm really into it at the moment. I just wish they would release it internationally with english subtitles since I suspect that from here on out you really need to understand what the hell is going on. I'm also too much attuned to the series and its ideas as well, since I had a notion that I mentioned solar powered submarines before, and lo and behold, I did so during season 2 when they found Shangri-La and the mass producing condors. I'm so into this series.