The forest consists of two parts, the part which is full of long and old trees and with their roots that exist everwhere. The other part, is the ancient castle that the royal family of Soleanna were living in, until the explosion of the Solaris Project. This part is guarded by special sentry, that offers trials, and the one who success in, will enter the castle through an Eagle. The forest is also shown to be in Mountainous, as there are several caves in it, and there two doors that, either connected to the "New City", or to "Soleanna Castle Town"
As the story that told in Sonic the Hedgehog, It was the place where the previous castle of the royal family were in, until the Solaris Project process that ruined all the castle, which leads the forest to be just for sightseeing object. In Sonic's story, Sonic's first infiltrating in the forest, was after defeating the Egg Genesis, to escape through the forest by Tropical Resort, however he later came to once again when he wanted to go to Kingdom Valley, after completing the three trials.
In Shadow's story, he went to, after completing White Acropolis, to get he and Rouge to the recovery point in the ancient castle. While not directory in gameplay, but Rouge, has also went to Tropical Resort. In Silver's story, he went, after his teleportation by Mephiles the Dark, to Sonic's timeline. He also did use of the forest to go to Kingdom Valley, after finishing the three trials. In the Last Story, both Elise and Sonic were going in the forest, however Mephiles used his Chaos Emerald to fool them, and from behind, he shot an energy emission at Sonic and killed him. After the final battle with Solaris, it is unknown what is the state of the forest.
It is the last Adventure field that Sonic is able to enter, as he must complete his entire Episode before he is allowed to enter the area (except during the short time when carrying Elise in it.)
Of all the Adventure Fields in the Game, it is the largest and as such one of the emptiest in the entire game.
If one causes a glitch to get Sonic into the area early, an area could be found in the center containing the 2-Dimensional objects that are used during the Race with Sonic Man and other Highway side-missions. There is nothing else one can do here, as the doors do not show up nor do level entrances if one does this glitch.
Of all characters to enter it, Shadow is the only one to not go through the Trials of Soleanna in order to reach his version of Kingdom Valley.
In the Archie comics issue 258, the forest zone appears under the name Soleanna Forest Zone.