Eggmanland appears in both the Wii/PS2 version and 360/PS3 version of Sonic Unleashed, where it is first seen in the opening cutscene before the player begins the stage of the same name. However, it can only be explored as a hub in the latter version after completing the game; in the former, that same area only appeared during its introductory cutscene.
In the Xbox 360/PlayStation 3 version of Sonic Unleashed, Eggmanland is a Town Stage that becomes available after clearing the game. Unlike most other Town Stages, Eggmanland serves as both its Town Stage and Entrance Stage, where the player can both access its Action Stage and Boss Gates as well as talk with townspeople and buy from shops.
The foundation for Eggmanland was laid during the beginning of Sonic Unleashed where Dr. Eggman schemed to harness the limitless energies of Dark Gaia to realize it. When the Earth was shattered by Dark Gaia when Eggman awoke it, Eggmanland was being built by a construction system powered by Dark Gaia's energies on a lone floating continent. However, due to Dark Gaia having dispersed across the globe, the construction of Eggmanland was significantly delayed. Eggman, however, devised a machine that attached Dark Gaia's fragments, Dark Gaia's Minions, to his location, speeding up the construction of Eggmanland.
At the time, Sonic the Hedgehog and Chip had restored the Earth's sixth continent, Eggmanland was completed. Soon after, Sonic and Chip came to Eggmanland to find the final Gaia Temple and fully restore the planet. There, Eggman welcome the duo over the speakers, before challenging Sonic to come and get him, much to Sonic's bemusement. As Chip sensed that the Gaia Temple was below Eggmanland, Sonic decided to tear it down to get there. Upon reaching the Gaia Temple at the bottom of Eggmanland, the duo restored Eggmanland's continent and afterwards both defeated Eggman and put Dark Gaia to rest. The state of Eggmanland afterwards is unknown, though, it most likely collapsed in on itself when the hole leading to the Earth's core that it was build upon was opened.
In the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics, Eggmanland is an energy refinery designed to resemble an amusement park with lethal attractions created by Dr. Eggman. When discovering the raw energies released by Dark Gaia during the Shattered World Crisis, the doctor designed Eggmanland as part of his plan to harvest and refine these energies.
Eggman has attempted to build Eggmanland numerous times in most games but has only accomplished this goal once.
The spelling of the name has varied widely; it is rendered Eggman Land in some pre-Unleashed games, whereas afterwards it always written Eggmanland. Sonic Unleashed itself uses four spellings - Eggman Land earlier in the script while it is in the planning stages, then Eggmanland referring to the built location, EggmanLand for the Wii/PS2 version's Day Stage, and finally Eggman-Land for the Wii/PS2 version's Night Stages.
As Eggman still preferred to refer to himself as Robotnik in dubs of Sonic Adventure, his ambition was to build Robotnikland on the ruins of Station Square. This was rendered obsolete when the Eggman name fully took over Robotnik, so subsequent games use the Japanese name.
As a bit of an inside joke, the three Egg Fighter citizens are named after abbreviations of three key game consoles (the Mega Drive, Dreamcast and Xbox 360) and the years in which their first Sonic games were released:
In the Xbox 360/PlayStation 3 version of Sonic Unleashed, after clearing the game, the last continent of the planet where Eggmanland is located at is not brought back into place. The PS2/Wii version has the continent restored back into place.
This is the only area in which there is no human Temple Guardian.