A Green Hill-esque area featuring many waterfalls and a dusk setting that gives it a romantic feeling. The higher ground is composed of wooden structures with varied patterns, some of them also repeating in the natural grassy floor in the lower levels. Palm trees adorn the foreground, with lamppost-esque structures among them.
Unique gimmicks here include water slides, tall segmented springs that recoil the player a short horizontal distance, Bungee Ropes, and vertical poles which the player can slide down and jump off of to either side using and the . There are also large, slow-moving floating platforms that can either assist the player in navigating the stage or crush the playable characters. Act 1 introduces water mechanics to the game, albeit requiring Knuckles to access.
Sunset Hill Act 3 ends with a boss fight against G-merl, repeating the same attack pattern as last time and going down in four hits (two on Easy mode). If this Act is completed with Sonic in the lead (although at this point, the only other possible combination would be Tails-Sonic), a cutscene will play. It will feature Sonic and Tails meeting Knuckles, who expresses his desire to support whatever are they doing, to what Sonic just says that they do not need any help right now. Knuckles, even angry at this, is unlocked for the main game and Time Attack modes.
The boss fight takes place in a circular arena. Dr. Eggman and G-merl will appear in a large wheel which comes rolling down the right-hand side of the arena. Eggman will laugh and then continue rolling; from this point on the character is vulnerable.