SonicN

Moon zone:
Collect all Chaos Emeralds by the end of the game, then play Sonic's X-zone. Successfully complete the zone to unlock the bonus Moon zone.

Chao Garden:
Successfully complete the game.

Hint: Fly high:
Play as Sonic (recommended), Miles, or Knuckles. Go to Zone 1 Act 1 and go to the area where the first loop is located. Stand on the sliver of land, then charge a Spin Dash for twenty seconds. Dash to the right and hold Down/Right. You will go down the hill (not getting all the rings). Eventually, you will go so fast that you will leave the screen. Sometimes it does not launch you off the cliff at the end.
Information in this section was contributed by stuart kadin.

Choose Amy, then go to Zone 1 Act 1. Go to the spring that is in front of the first loop. Stand in front of the spring, then do the Hammer Jump. If done correctly, you should go very high.
Information in this section was contributed by Mspyder2f2f.