The Gaia Gate (ガイアゲート,Gaiagēto?) is a type of portal that appears in Sonic Unleashed. They are ancient devices found on each continent on Sonic's world. They were created ages ago and act as transporters to the different areas on their respective continents. In gameplay, the Gaia Gates serve as entrance points to the game's Action Stages and Boss Stages.
On the PlayStation 3/Xbox 360 version of Sonic Unleashed, the Gaia Gates are circular teleportation pads that emit a glowing cylinder of light. On the PlayStation 2/Wii version however, the Gaia Gates are large structures resembling temples with several doors inside. Each of these Gaia Gates has its own theme matching the continent it represents (Holoska's Gaia Gate has ice all over the place while Adabat's is overgrown with flora).
The Gaia Gates are tied to Light Gaia and appear to be powered by him.
On the PS3/Xbox 360 version of Sonic Unleashed, the Gaia Gates can be found inside the Entrance Stages. These Gaia Gates come in two types; the Action Stage gates and the Boss Gates.
The Action Stage gates specifically lead to the game's Action Stages. The Action Stage gates where Sonic the Hedgehog is playable are orange with a sun icon and can only be accessed during the day, while the Action Stage gates where Sonic the Werehog is playable are blue with a moon icon and can only be accessed during the night. Most Action Stage gates are unlocked in accordance to the story progression, but there are also additional, non-obligatory, ones that can be unlocked by collecting enough sun medals or moon medals.
The Boss Gates specifically lead to the local boss, and are the ones that lead to the Gaia Temples. These Gaia Gates are usually red and are marked with Dark Gaia's symbol, and can only be unlocked by assembling their Gaia Keys.
In the PS2/Wii version, the Gaia Gates are found on the local continents' village maps under the name Sacred Shrine. These areas are the only hubs in the game that can be explored in 3D. However, only Apotos Gaia Gate can host Sonic the Hedgehog; all the others transforms him into Sonic the Werehog upon entry.
To access a local Gaia Gate, the player must obtain a Sun Tablet/Moon Tablet by talking with the villagers, which will make the Sacred Shrine appear on the map. Inside the Gaia Gate are several doors for the player to open. Several of these doors can be unlocked by collecting enough sun medals or moon medals. Behind them are hidden rooms with puzzles revolving around using (or avoiding) shafts of light that will temporarily transform the Werehog back to Sonic, where the player can obtain hidden items such as extra lives, collectibles and bonus missions.
At the back of each Gaia Gate are up to three types of doors that lead to the game's Action Stages and Boss Stages. The Action Stage doors where Sonic the Hedgehog is playable have a sun icon and can only be opened with a Sun Tablet, while the Action Stage doors where Sonic the Werehog is playable have a moon icon and can only be opened with a Moon Tablet. The doors that lead to the Boss Stages, and as well the local Gaia Temple, have a star pattern and can only be unlocked with the Planet Tablet. Note that not all Gaia Gates have all three doors: Apotos only has Action Stage doors, and Mazuri only has a Boss Gate door.
These versions of the Gaia Gates are all connected. The player can enter a Gaia Gate from another by stepping on one of the glowing pads in the room on the left of each entrance.
In the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics, the Gaia Gate is a magical location hidden within Apotos and is described as the single most important location in the world. The only person who knew of its existence was the sage Gregorios. From the Gaia Gate, the visitors are able to enter the central chambers of all seven Gaia Temples
When he was nearly assaulted by Metal Sonic, Gregorios broke his vow of secrecy and revealed the Gaia Gate to the New Freedom Fighters so they could use it for the benefit of the world before Dr. Eggman could uncover it.
On the PS2/Wii version of Sonic Unleashed, Apotos is the only Gaia Gate that doesn't cause Sonic to transform into the Werehog in the main hall.
Playing with this reveals that it is not possible to cause the game to register a Drift bonus, even if drifting is utilized for an extended period of time.
Also, on the PS2/Wii Version of Sonic Unleashed, Eggmanland is the only location without a Gaia Gate.
In some of the Gaia Gate missions in the PS2/Wii version, Sonic is required to ring dash across certain gaps. The rings used here are unique as they regenerate shortly after being collected. This can be abused to gain boost power (though the boost is never needed).
This reveals that it is not possible to level up even if the ring quota to do so is met. However, three full bars of boost can be obtained.
Sonic can boost towards the screen. This is impossible in the regular day stages.
If Sonic transforms into the Werehog and back, he loses all his rings and boost.
A glitch exists in the PS2/Wii versions. If Sonic crawls around (during missions while he is in normal form) he will never change back to the Werehog. Even if the purple aura begins to show, crawling causes it to go away.