Tolbi has become Weyard's most metropolitan town because of annually hosting the Colosso festival: its tournament is the foremost event for warriors across Weyard. Furthermore, the larger festival is the biggest hot-spot for tourism in the world; visitors from several continents all come to take-part in the festivities. Colosso was conceived and established by the lord of Tolbi, Babi, for personal reasons not known to the public. The festival includes many things set up as attractions, such as the Lucky Medal game at Tolbi Spring, the slot-machine-esque Lucky Wheels game that uses game tickets given out by shopkeepers around Weyard, and the casino-like Lucky Dice. But the event that has become synonymous with the name "Colosso" is the tournament of warriors that takes place in huge stadiums physically connected to Babi's Palace, and these stadiums are accessible by either walking into the main Colosseum Entrance or by travelling through the Colosseum Tunnel to reach the bleachers. Babi himself, along with his chief minister Iodem, uses this tunnel to come to a throne at the head of the stadium to look upon the competition.Colosso Gladiators to proceed to the Colosso Finals, which is a series of races whose stage layouts test both physical ability and momentary cunning. Each year, the gladiators strong enough to win or come close to the championship are offered positions as soldiers and bodyguards in Babi's Palace; indeed, the solders seen under Babi's employ in Golden Sun are champions of prior Colosso events, or at least have placed high enough to receive Babi's approval. And even if warriors do not actually achieve the ultimate goal in Colosso, their participation in Colosso is beneficial because demonstrating their strength to the public in this fashion increases their reputation, which helps them contract jobs as mercenaries or bodyguards or other such positions.
Colosso's tournament itself is also a pure spectator's event. The Trials alone take place in a giant stadium whose bleachers are inevitably filled up, and each of the finals matches take place in specialized arenas that end up filled with spectators on the sidelines. Since the event is so major, even scalping is made a business among the people, where people buy seats in advance and sell seats to spectators at increased prices. Spectators also get to play a lottery-style game called Lucky Guess during each year's Colosso, where they bet on which of the Colosso gladiators will win the championship, similar to real-world horse racing betting.
 Colosso Finals
- Main article: Colosso Finals
The Colosso Finals competition takes place after the Colosso Trials and is, effectively, the main event of the entire festival. The Finals are comprised of three series of stages that have simple puzzles integrated into their layout, and the seven highest ranked Colosso Gladiators from the Colosso trials face off in these series of puzzle-like races where they eventually meet in a central arena and engage in one-on-one duels. This is a major gameplay episode in Golden Sun that occurs after completing Altmiller Cave, and when Isaac competes in them as an additional, eighth fighter, he must win at least the first two matches to earn a conversation with Lord Babi and thus proceed with his quest.
At the time of Golden Sun, Babi was already over 150 years old. This did not occur naturally; long ago, Babi and his friend Lunpa were caught up in the Great Flood and ended up amidst the mythical island society of Lemuria, whose Mercury Adept inhabitants live for centuries thanks to an Alchemy-based influence that pervades the city. The Lemurians had a stockpile of Lemurian Draught they would take with them in ancient times on expeditions outside the Sea of Time; the draught allows anyone who drinks it routinely, Adept or not, to live well beyond his or her normal years, even far away from the similarly-age-slowing waters of Lemuria Spring. Although Lunpa remained behind, Babi ended up fleeing the isle on a stolen Lemurian Ship and the whole stockpile of draught. His draught would allow him to live long enough to rule the town of Tolbi in Gondowan for over one hundred years, during which he presumably created the annual Colosso festival, which helped make him and his town among the most powerful in Weyard.
Babi cemented Colosso's worldwide popularity with its central event, a large-scale and prestigious tournament of warriors. Babi would realize in his later years, however, that his stockpile of life-preserving draught, which he kept in an ancient, alchemical vault in the depths of Altmiller Cave, would not last him forever. Babi figured the only way for him to keep on living was to somehow get back to Lemuria and fetch another stockpile of draught. Lemuria, however, is effectively impossible to enter by conventional sailing methods because its area of the ocean, the Sea of Time, is surrounded by whirlpools and stone crags that would easily destroy wooden ships that try to sail through there. And even if the ship would survive, there are currents that would change a boat's direction subtly but tangibly enough that they would prevent would-be sailors from keeping a straight course on their ships. So, Babi sought remedies for each of these problems.Babi Lighthouse on the northeastern tip of Gondowan – the point on Gondowan closest to the foggy Sea of Time – so that its light could shine bright enough that sailors sailing into Lemuria will be able to keep their bearings. The other remedy was what Babi hoped to achieve by hosting Colosso itself: find capable warriors who exhibited the same Psynergy powers as the Adepts he encountered in Lemuria. Only Adepts could helm the Lemurian ship he stole because it runs on Psynergy power, and only a Lemurian Ship is sturdy and reliable enough to safely make its way through the Sea of Time into Lemuria. While Babi himself was not an Adept, he had learned a little Psynergy during his stay in Lemuria, which allowed him to commandeer a Lemurian Ship and leave Lemuria over a century prior to Isaac's arrival in Tolbi. By the time of Golden Sun, during that year's Colosso season, Babi Lighthouse was close to completion, and Babi's draught stockpile had nearly been entirely consumed.
As the year's Colosso Trials began, Babi headed off into Altmiller Cave to fetch the last of his draught, but since he had been attempting to ration his drinks to extend his lifespan, he was weaker than normal and eventually collapsed in the cave. It was at this time that fate intervened and Isaac's traveling group of Adepts happened upon him while exploring the cave. They rescued the invisible lord from an eventual death by using their Psynergy powers to retrieve for him his very last draught from the bottom of the cave. Grateful, Babi saw Isaac as the possible miracle warrior he desired to pilot his Lemurian Ship for him, and he decided to enter Isaac into the Colosso Finals so that he may observe the full extent of Isaac's Psynergy powers in battle.
By then many people in Tolbi had noticed that Colosso had been lasting longer than it usually does, but once Babi returned to his throne at the Colosseum, the Finals began in earnest. Nomally, seven warriors compete as the finalists as Colosso Gladiators, but for the first time in Colosso history an eighth warrior, Isaac, was personally entered by Babi himself, to the mixed reactions of the spectators at Colosso. In the event, Isaac performed startlingly well in the eyes of the spectators, but Babi and his chief minister Iodem knew that it was his Psynergy-enhanced battle abilities that are the real miracle at play. The third match was especially difficult, and whether Isaac won or lost the battle, he collapsed from exhaustion right in the stadum after the end of the bought, and fell asleep then and there before spectators looking on in awe. In the event Isaac won the battle, Babi and Iodem found it most rewarding to see Babi's favored warrior steal the day, and they would afterward present to Isaac Colosso's victor's prize, the Lure Cap. Isaac would also gain some fame as a warrior that influenced later events in Golden Sun: The Lost Age.Lalivero, his tower of Babi Lighthouse and the ancient Venus Lighthouse, climb the either Lighthouse and gaze upon the Sea of Time, and then make an attempt to reach Lemuria so that they would be able to retrieve more Lemurian Draught for him. Isaac and his party set out on their newly multi-layered quest, but in Golden Sun: The Lost Age they were ultimately unable to enter Lemuria without some ancient weapon known as a trident, and Babi passed away from old age, deprived of life-preserving draught. Upon hearing the news, Isaac decided to direct his efforts thus back towards his quest of saving his friends Jenna and Kraden and stopping the lighting of the Lighthouse beacons. It is unknown what happened to the Colosso festival afterward Babi's death, though it is generally assumed that the festival and tournaments continue on each year under new leadership, possibly by Iodem.
 In The Lost Age
If Isaac won the Colosso tournament he participates in, and the player transfers their data from Golden Sun to The Lost Age, the three Colosso Gladiators that he defeated in battle, Azart, Satrage, and Navampa, will cavort together and conclude that Isaac's match must have been rigged; they decide to seek Isaac out across Weyard and attempt to pay him back by defeating him in battle. Morgan and Dekka, other competitors, also seek revenge on Isaac, but never find him. Another competitor, Galahad, overhears these vengeful plans and, he too, sought Isaac, though instead to warn Isaac about the possible ambush. Galahad would meet with Felix in the Osenian village of Mikasalla, where he would ask Felix to pass on the message should he meet up with Isaac. Azart, Satrage, and Navampa eventually do catch up with Isaac in Shaman Village Cave in Hesperia, after Isaac and his party have joined forces with Felix's group, and attempt to defeat the Warriors of Vale in a three-on-eight battle. Perhaps not surprisingly, they lose, and they admit they were wrong in assuming Isaac didn't win Colosso fair and square, since, as Kraden explains, Psynergy is a warrior's talent. They receive Isaac's forgiveness and give him the unique Golden Shirt they found in the cave earlier, and declare they hope to be strong enough to win against him in the next Colosso.