Sonic The Hedgehog: Special Zone entrance
You can almost always have the Special Zone entrance open (the giant ring next to the sign at the end of level Acts 1 and 2) by not losing your rings. If you do lose your rings, when you pass a checkpoint, intentionally die, then continue through the level without losing any rings. This works about 80% of the time.
Collect 50 rings and finish the stage. There will be a giant ring.