A city-state of its own, Soleanna has a monarchy as its government and is currently ruled by Princess Elise.
The people of Soleanna worshipped the god Solaris as their patron deity and held an annual ceremony to ask for its loving light and not its destructive fire. After Solaris was erased from existence, it is unknown if this tradition is still being upheld.
Soleanna features an old library that contains documents and records of civilizations that have risen and disappeared since its establishment, such as a book written in ancient Babylonian with information on the location of the key to the long-lost Babylon Garden.
The city of Soleanna was build nearly 12,000 years ago as a part of the Hidden City Initiative where mankind tried to build hidden cities that would allow them to survive the Xorda Attack on Earth. After Soleanna was built, a fraction of the human population was evacuated there before the Xorda attacked with their Gene Bombs.
Over the next several thousands of years, Soleanna served as the self-sufficient home to the human population living there. As Earth, later renamed Mobius, continued to change following the Xorda's attack, Soleanna and the other cities created by the Hidden City Initiative eventually established a network of communication and trade, forming the United Federation, with Soleanna a member of it.
Ten years prior to the current storyline, the Duke of Soleanna and his researchers experimented on Solaris in Soleanna's research labs in an attempt to harness its time-warping powers. Instead, their experiments split Solaris into Mephiles and Iblis, who were sealed away inside the Scepter of Darkness and Elise respectively. In the present day, Iblis and Mephiles were freed and rejoined to form Solaris, but the malevolent deity was stopped by Sonic the Hedgehog and his allies.
- On a clear day, Soleanna can be seen from the top of the Guardian Mountain, according to Hope.