There are several themed "Zones" to play through in Sonic the Hedgehog.
Each one consists of three "Acts" and the third Act ends with a unique boss battle. The exception to this is "Final Zone" which only has one Act which is a boss battle in its entirety.
The Zones are:
- Green Hill Zone
- Marble Zone
- Spring Yard Zone
- Labyrinth Zone
- Star Light Zone
- Scrap Brain Zone
- Final Zone
There are also Special Stages which are activated by collecting 50 or more Rings in a single Act, then jumping into the giant ring which appears beside the final sign post at the end of the Act. The Special Stages are 2D puzzles in which you must try to collect a Chaos Emerald. Collecting all of the Chaos Emeralds unlocks the game's second ending.
