The Gaia Temples (ガイア神殿,Gaia Shinden?), also known as the Temples of Gaia, are structures that appears in Sonic Unleashed. They are a set of seven ancient temples that are located around the world. With the aid of the seven Chaos Emeralds, these temples can bring the world back together when it is broken into pieces by Dark Gaia during the time of awakening. They have a strong connection to Light Gaia.
The Gaia Temples are immensely large temples in various shapes. Their function is to harness the very power of the planet itself and work in sync with the Chaos Emeralds, with the purpose of putting the world back together whenever it is broken into pieces by Dark Gaia and ultimately seal up the beast itself.
The process of restoring the planet is through placing one of the seven Chaos Emeralds in a small altar in the center of the temple. The Emeralds' power will then provide the energy for the Gaia Temples to help the Earth heal naturally from Dark Gaia. In the case the Chaos Emeralds have been drained of their power, placing them in the alter will cause the Emeralds to be recharged through the planet's power. In turn, the act of the Emeralds being recharged leads to the equal and opposite reaction of the Emeralds healing the planet.
Since Light Gaia has been the one performing the process of restoring the planet since the beginning of time, it is unknown whether the Gaia Temples have always been used by Light Gaia to restore the planet since the beginning of his conflict with Dark Gaia (meaning they date back to the dawn of time) or they are only relatively new constructions made by unknown builders.
Chip shares a special connection with the temples since they share the job of restoring the planet's condition, and they act as extensions of Chip himself. With Chip's innate powers, he can activate their central altar for the Chaos Emerald to be placed and sense the location of the temples. It is within Adabat's Gaia Temple that his memory is restored by finding an apparent fragment of his essence inside it. As seen during the battle against Dark Gaia, Chip is able to call the Gaia Temples to his location in times of self-defense in order to form the Gaia Colossus.
The Gaia Temples were created ages ago to house the earth's power. Who or what created the Gaia Temples and for what purpose are unknown. The location of each Gaia Temple were recorded in the Gaia Manuscripts following the time of awakening that occurred some tens of thousands of years ago.
In Sonic Unleashed, Dr. Eggman learned about the Gaia Temples from the Gaia Manuscripts. After somewhat successfully awakening Dark Gaia with his Chaos Energy Cannon and splitting the earth apart, the doctor sought to secure the Gaia Temples as they could prove to be a threat to his plans. Meanwhile, Sonic the Hedgehog and Chip (aka. Light Gaia) began to seek out the Gaia Temples in order to restore the planet and stop Dark Gaia's resurrection. When Eggman learned Sonic was still alive after their last encounter, he deployed his forces to the Gaia Temples to slow down Sonic while completing his plans with Dark Gaia's energies. These efforts proved to be in vain, as Sonic and Chip were successful in reaching all seven temples, stopping the doctor's plans and putting the world back together.
In the process of the restoration of the final continent, the Gaia Temples were called together by Chip to form the Gaia Colossus for Chip's battle with Dark Gaia. All of the Gaia Temples (still combined into the Gaia Colossus) were later seemingly destroyed when Chip got resealed inside the earth's core following the defeat of Perfect Dark Gaia.
In the Wii/PlayStation 2 version of Sonic Unleashed, each Gaia Temple (except for the one in Eggmanland) has one or more appointed human guardian who watch over them and choose those worthy to enter. The guardians are also the only ones who can assemble a Planet Tablet, the key to the Gaia Temples.