Wood Zone is a wood-themed level created by Brenda Ross that is present in the Sonic 2 (Simon Wai prototype). It hosts flora and fauna in its backdrop, and an elaborate maze of trees in the foreground. The level is very unfinished: in the Simon Wai prototype, the first act ends rather quickly, and the second act is simply an empty level slot with a palette.
The music that plays in the working version of the zone is very similar to that of Metropolis Zone, and is actually the same music used in the beta Metropolis Zone. For a long time, the music connection made people question if this zone was a supposed "past" version of Metropolis Zone, like Rock Zone was a past version of Dust Hill Zone. Though with the reveal of many scrapped concepts in May 2017, this theory was put to rest. Instead, Wood Zone was supposed to be the present version of Casino Night Zone, which was itself in the medieval time-frame.
The level seems to have been worked on after the Simon Wai prototype, as new background scrolling data is present in revision 00 of the game (a much later build). Through hacking, Wood Zone can be accessed in Zone slot 02 of the final Sonic 2. A Game Genie cheating device can also be used to access Wood Zone in the final version. Use the code ACLA-AECY (AB6X-AEBR in Knuckles in Sonic 2). Then go to the stage select menu and select Emerald Hill Zone (Special Stage in Knuckles in Sonic 2). Unlike Hidden Palace Zone, very few parts of Wood Zone remain in the final game: only the palette and music data are present.
Wood Zone was subject to much speculation for many years. It became a fan favorite, perhaps as well known as the Hidden Palace Zone, and has been featured in several hacks. Two notable hacks, Sonic 2 Delta and Sonic 2 Long Version, each contain fan created versions of what their creators thought the zone might have looked like had it been completed.
The idea of a forest-themed level was used later in Mushroom Hill Zone in Sonic & Knuckles.