IceCap Zone
From Sonic Retro
Icecap Zone is the fifth zone in Sonic the Hedgehog 3 (as well as in Sonic & Knuckles).
It contains an outer "snow" level and an inner "cave" level, and uses a background-changing effect to switch between those.
The zone is theorized to have been based off of Sonic 2's Hidden Palace Zone, as the bridges and glowing orbs underground resemble those of Hidden Palace.