Giant Ring
From Sonic Retro
A large ring that appears in Sonic the Hedgehog 3 and Knuckles. It teleports you to a special stage; or if used while in the S&K zones of Sonic 3 and Knuckles, will transport you to Hidden Palace.
Giant Rings also appear at the end of acts in Sonic 1 if you have collected 50 or more rings. They teleport you to special stages as well.