North Cave is a location that appears in the Sonic the Comic series published by Fleetway Editions. It is a cave located within the Frozen Zone, a freezing cold section of South Island, where Sonic first hid the six Chaos Emeralds from Dr. Robotnik.
They were safe in the North Cave, the cold temperatures kept the Emeralds stable, until Captain Plunder stole them. After Sonic retrieved the Emeralds, he kept them in a special sub-zero temperature box in his secret base. Thus their location became a mystery once again.