Frozen Factory: Zone 4
Red Star Ring 1: When you come to a boost at the beginning of the level, jump over it and onto the raised platform behind it. The Red Star Ring is on the next platform after that.
Red Star Ring 2: Impossible to miss, the second Red Star Ring is at the end of a line of rings midway through the level's first 3D sequence.
Red Star Ring 3: Another one that's difficult to miss. This one is near the end of the second 2D segment, in the middle of a room full of pink octopi.
Red Star Ring 4: In the area in which you need to proceed upwards by turning the nuts, keep to the left and find the fourth Red Star Ring tucked into a little alcove in the center structure.
Red Star Ring 5: After returning outdoors, you'll pass through five pistons in a row, and then a loop. After a long jump, you'll land on a sheet of ice. Jump and press the Y button to pound through the ice to the pistons underneath, on top of which you'll see the Red Star Ring.