It is the 16th century. From all over Europe, great ships sail west to conquer the New World, the Americas. The men eager to seek their fortune, to find new adventures in new lands. They long to cross uncharted seas and discover unknown countries, to find secret gold on a mountain trail high in the Andes. They dream of following path of setting sun that leads to El Dorado, and the Mysterious Cities of Gold.
The Mysterious Cities of Gold (Japanese name: Taiyo No Ko Esuteban, French name: Les Mystérieuses Cités d'or), is a Franco-Japanese co-production dating to 1982. The show is animated in a style that's a distinct combination of Japanese and Western animation, features a long, continuous storyline, and has a dedicated and loyal fanbase.
It was aired in several countries, and was shown in the United States on Nickelodeon during the late 1980s.  Despite its similarities to Avatar: The Last Airbender -- including being shown on the same network -- The Mysterious Cities of Gold was notable in its disregard of Never Say "Die" and Gosh Dang It to Heck, two tropes which have dogged American cartoons well into the present day. In some countries where this series was shown (although not in the United States), each episode was followed by a short documentary exploring subjects related to the episode. The documentaries were funded by the NHK.
The year is 1532, a time of exploration (and exploitation) of the New World. The prize foremost in the mind of every Spanish Explorer is the Mysterious Cities of Gold, said to lie deep within the heart of the South American continent. Of course, none of this means anything to Esteban, a young orphan currently living in Barcelona under the care of the Church.
The boy knows very little about his past -- his only connection to it being a strange, crescent-shaped locket he's had since being brought to Barcelona as a baby and a mysterious ability to summon the sun on cue (thus earning him the nickname "The Child of the Sun.")
But all that is about to change...
One day, when Esteban is out and about in the city, a charismatic explorer named Mendoza crosses his path. He later claims to be the man who brought Esteban to Spain from the New World after rescuing him from death at sea. To prove this claim, he produces a round ornament that fits perfectly into the boy's locket. Mendoza offers to take Esteban on his next journey of exploration to the New World where the boy will presumably get the chance to learn more about his birth parents. Of course, Mendoza's intentions aren't entirely altruistic and in the boy's interests, as it's the explorer's belief that Esteban's locket and strange powers are somehow connected to the Mysterious Cities of Gold, which he hopes to find.
Esteban accepts the Call to Adventure and heads for the New World, but he quickly learns that Mendoza may not be entirely worthy of his trust. Proof of this lies in the fact that Mendoza has kidnapped an Incan girl (who had been taken to Spain and given to the Queen years before) and stowed her away on the ship they're currently travelling on. The girl, named Zia, has the ability to read knotted strings called quipu -- an ability which Mendoza and his employers hope will come in handy on their quest for the Mysterious Cities. Esteban quickly bonds with Zia after discovering, to his amazement, that she has a locket that looks identical to his. Could she somehow have a personal connection to the Mysterious Cities of Gold as well?
During his journey to the New World, Esteban meets many more interesting people, including Mendoza's servants, the Plucky Comic Relief duo, Sancho and Pedro, and Tao, an island boy whose ancestors were (he claims) an advanced civilization capable of great magical and technological feats. The trio also come across The Golden Condor, a solar powered, gold-plated, bird shaped airplane built by an ancient civilization. Esteban also encounters some fearsome enemies, like the Spanish military commander Francisco Pizarro and the Olmecs, a tribe of elf-like humanoids who want to use the power of the Mysterious Cities of Gold to Take Over the World. The trio of kids must use their wits, skill and bravery, along with Mendoza's Badassness to unlock the secrets of those mysterious Cities of Gold and their relations to them.
The Mysterious Cities of Gold is a sprawling adventure epic that is well worth a watch. A Region 2 English DVD release was brought about in the UK in June 2008, and a French movie company is currently planning a film based on the TV series. A Region 1 English DVD was released in April 2009.
A sequel series was recently announced consisting of three seasons with 26 episodes each. This sequel supposedly deals with Esteban's further adventures in finding the other six cities of gold. Season one is set to premiere in September 2012 on TF1.
There was also an attempted retool by a different animation company in the mid-aughties, which featured very different character redesigns, the removal of some characters (Tao being one of them), the addition of new characters, and choppy animation. It was not well-received and was subsequently abandoned after a limited DVD release in France.
This series can be seen on Netflix. At last!
The Mysterious Cities of Gold provides examples of:
- Adaptation Distillation: The TV show was theoretically adapted from a novel which actually has very little in common with it; it especially lacks the Speculative Fiction elements and Kid Heroes.
- Adults Are Useless: The adults in this show are either incompetent or, in the case of Gomez and Mendoza, merely being outsmarted.
- I'm not sure Mendoza is ever outsmarted, although early on he does overestimate how much the kids (Zia and Tao in particular) believe they are dependent on him.
- Adventurer Archaeologist
- After the End: Atlantis and Heva fought a war that ended with the use of the "weapons of the sun", which are implied to be akin to nuclear weapons in terms of destructive power.
- Alternate History
- The Amazon: Much of the story takes place here.
- Ancient Tradition: The Guardians of the Mysterious Cities.
- And Knowing Is Half the Battle: The mini-documentaries shown after the episodes are possibly the greatest example of this trope (very long, accurate, an actual budget)... But also it's subversion. The one about human sacrifices is nothing but traumatizing. It ends with a first-person shot of a victim tied up on a sacrificial altar. You see the priest, on top of you, lifting up his knife and stabbing you. The screen suddenly fades to black. Then the narrator says "see you next week on another episode."
- How about the one where they show the chicken's head being hacked off with a machete, then the headless corpse flapping and bouncing around madly in the dirt?
- And the Adventure Continues...: The series ends with Esteban, Tao and Zia setting off on the Golden Condor to find the remaining six Cities of Gold.
- Animated Series
- Applied Phlebotinum
- Atlantis: The ancient civilization of Heva/Mu fits this trope, although it also fought the literal Atlantis in a war thousands of years ago, which both sides lost.
- Badass Cape: Mendoza's, of course.
- Badass Spaniard: Mendoza
- Because Destiny Says So
- Beethoven Was an Alien Spy: The origin and downfall of the Olmecs.
- Beginner's Luck
- Beneath the Earth: Where the Morlock-like Olmecs dwell.
- Butt Monkey: Gaspard (and thoroughly deservedly).
- Cave Behind the Falls: Which leads to Macchu Picchu.
- The Chick: Zia
- The Chosen One: Esteban
- City of Gold: What the characters are searching for. Duh!
- Competence Zone: Subverted; the considerably older Mendoza is the most competent member of the group, as befitting of a seasoned explorer with years of experience. The children often look to him for guidance and leadership.
- Cool Boat: The Solaris
- Cool Plane: The Golden Condor
- Cue the Sun: Esteban has the ability to call forth the sun.
- Cut Lex Luthor a Check: Despite chasing after the treasures of the Mysterious Cities of Gold, not a single one of them ever considers that a fast automated ship armed with a frigging laser, or frigging flying machine might actually be worth more!
- Debut Queue
- Distressed Damsel
- Lana, from the floating Totola village, who had been abducted by the Urubus in order to be sacrificed to Pachamama.
- Maina, Papacamayo's adoptive daughter, who is abducted by the Olmecs.
- Zia spends a good part of the plot as this. Heck, the entire reason she joins the plot is her being kidnapped. First brought to Spain, then kidnapped back from Spain to South America.
- Dramatic Wind: Mendoza and his cape.
- Dub Name Change: Heva was originally called "Mu".
- Pichu was renamed Kokapetl, and the title basically changed from "Esteban, Child of the Sun" to "The Mysterious Cities of Gold."
- Dumb Muscle: Teteola, the Doctor and Malinche's henchman.
- Durable Deathtrap: Traps in the ruined temples.
- Even Evil Has Standards: Malinche suggests poisoning a village to get at the gold in the lake as well as to keep the kids from being sacrificed. The doctor's response to this suggestion is, "What?!" and says he hates doing it -- and even then, he only mixes the poison.
- Everyone Calls Him "Barkeep": Esteban's father, who is just referred to as "The Traveling Prophet".
- Everything's Even Worse with Sharks: It wasn't enough that Esteban, Zia, Mendoza, Sancho and Pedro were stranded on a flimsy raft in the middle of the ocean. They had to be attacked by sharks as well. (Proving how much of a Badass Spaniard he is, Mendoza manages to kill one virtually barehanded).
- Evil Chancellor: Omuro, great priestess of the Amazons.
- Forgotten Phlebotinum: Tao's jar.
- Gadgeteer Genius: Tao
- God Guise: Esteban is believed to be a God by various New World tribes.
- Gold Fever
- Gondor Calls for Aid: The entirety of episode 33, "The Reunion", is this trope played out as the various villages are convinced to help the Village of the New Sun fight the Olmecs.
- Gosh Dang It to Heck: Averted with lines like, "Damn your eyes, FIRE!" and "Straits of Hell". Although it is worth mentioning that in the right context, you can get away with "Hell" in a kid's work. Heck, Sleeping Beauty has a "G" rating despite that word.
- Great Big Book of Everything: Tao's encyclopedia of plot exposition.
- Heroic Sacrifice: Esteban's father, who dies in his attempt to prevent an Applied Phlebotinum China Syndrome. According to Word of God, he somehow survives and meets Esteban again. We'll count it: onscreen he's toast.
- Heel Face Turn: Mendoza, while not really evil or greedy, does eventually warm up to the kids.
- Historical Fantasy
- Historical In-Joke: Several characters, like Pizarro and Mendoza, are based on historical people. Also, the term "Children of the Sun" is the name the Incas sometimes called themselves. "Child of the Sun" was a title given to a Spanish man named Alvarado, Cortez's right hand man by the Indians.
- Hostage for Macguffin
- Hot Amazon: A G-rated version. The topic of how the women replenish their numbers never comes up.
- Ho Yay: A Puppy Love version with Esteban and Tao, who cling to each other when stressed or frightened, invade each others' space at any time for any reason, and generally behave like a married couple. Also, when Tao was forced to destroy the Solaris, only the sight of Esteban calling to him could cheer him. Also: Sancho and Pedro for the adult version, or Gaspar and Gomez for the villain version.
- Humongous Mecha: The Olmec War Machine.
- Inevitable Waterfall
- International Coproduction: Between Di C, N.H.K. and Studio Pierrot.
- Kid Hero
- Knight Templar: Menator
- Landmark of Lore: Machu Picchu, although it was never directly stated as such in the show. Also the Nazca lines, which in this universe are the pre-determined autopilot routes for the Golden Condor.
- Last of His Kind: Tao
- Limited Wardrobe: Esteban is the only one that got a costume change and that was early in the show. One would think trekking through the jungles, deserts, and seas, would those clothes be reeking of gunk by the end of the show. Gaspar and Gomez still have one costume each but at least theirs show a little wear and tear. Mendoza somehow manages to maintain his cloak.
- That doesn't even count, his seafaring clothes just got torn up after the Esperanza's wrecking, and by the time he got to Tao's island he simply discarded his red vest to end up in the damaged outfit he'd wear for the remainder of the show.
- Lost Technology
- Lovable Traitor: Mendoza
- Loyal Animal Companion: Kokapetl
- Magic Skirt: Zia and Tao
- Mayincatec: This series is a classic example of Mesoamerican Hollywood History.
- The Messiah: Esteban
- Mis Blamed: Some differences between the French and Japanese translations are attributed to Bowdlerization by the former of the latter, which is inaccurate since the series is a joint Franco-Japanese production written by Jean Chalopin and Bernard Deyriès but animated in Japan. If anything, the differences were more to tailor them to differing expectations of their respective 80s-era audiences than anything else.
- Mutants: Many viewers think the Olmec are aliens but the way the Olmecs describe themselves makes them being mutants much more likely.
- Notable Original Music: The theme song and BGM was composed by the musical team of Shuki Levy and Haim Saban. The music was collected and released vinyl and then on DVD in France. 
- How this has not been promoted to Crowning Music of Awesome is beyond my ken. The entire soundtrack not only fits perfectly, it also never seems overly repetitive through 39 episodes and practically every motif is memorable.
- Older Is Better: How the tech of the series literally runs.
- Opening Narration
- Parental Abandonment
- Phlebotinum Breakdown: The Golden Condor uses solar energy to fly. Which is great, except when it's nighttime or the sky is overcast.
- Post Episode Trailer
- Precursors: The Hevan/Mu civilization
- "Previously On..."
- Prophecy Twist: It was prophesied that one of the Cities of Gold would be destroyed by "white men". It turns out these white men were the Olmecs not the Spainards.
- The Quest: Which is to find the Cities of Gold.
- Quirky Miniboss Squad: The heroes have two sets of these following them around, Commander Gomez and Gaspar, and Malinche and The Doctor , trying to beat them to the treasure.
- Silly Reason for War
- Skinny Dipping: In one episode, Esteban takes a bath naked in the river, since swimsuits hasn't been invented yet. He forcefully drags a reluctant Tao to come along, but didn't invite Zia.
- The Smart Guy: Tao
- Speedy Techno Remake: Golden Condor vs. The Olmec Machine
- Supporting Leader: Mendoza
- Team Pet: Kokapetl (called Pichu in French)
- Temple of Doom
- Those Two Guys: Sancho and Pedro
- Three Amigos: Esteban, Zia and Tao
- Title Theme Tune: (Ahhh-ah-ah-ah) Someday we will find the Cities of Gold! It's also an Ear Worm.
- A generic J-pop song , as well as MIDI samples as BG music in the original Japanese. It flopped miserably.
- Tripod Terror: The Olmecs' three-legged flying machine, which is also capable of walking.
- Verbal Tic
- Walking the Earth
- Walking Disaster Area: All the temples visited by the heroes end up destroyed.