Ghost Town is the third stage of Sonic Forces and the introductory stage for Classic Sonic. It's a completely new stage, set in the same city featured in the second cutscene of the game, now totally destroyed, ablaze and terrified by the Eggman Empire's domination.
In terms of plot, after the formation of the Resistance, Tails feels lost without the presence of Sonic and is separated from the group with no contact. Amidst the chaos of the city, Tails finds E-123 Omega and tries to repair him, not realizing that he is being observed by Chaos, who tries to attack him, making the fox cower in fear and call for Sonic's help. Nevertheless, the God of Destruction is stopped when Classic Sonic arrives via interdimensional portal and jumps on his head. Tails imagines that he was saved by Sonic, but soon realizes that it is actually a different version from another dimension. Nevertheless, this helps him regain his hope, and the two set out to save the world together.
Ghost Town, being the first stage for Classic Sonic, is infested with Hint Rings in certain areas to assist the player. The stage itself is short but has several paths, with some rewards such as Shields or Invincibility monitors hiding under some platforms. While the path above shows the burning ruins of the City, the underground path goes through the sewers with simple platforming sections.
This stage shows a scenario of complete chaos and war in the background, with structures, buildings, houses, among others being destroyed by hordes of Death Egg Robot sentinels and other Eggman Empire robots. Overall, the city's structure has influences from some real cities like San Diego. The bottom mountains and hills of Green Hill can also be seen in the background; plus it is a coastal region.