Presumably the Zone, as seen from Citadel Robotnik. Art by Roberto Corona and Steve White.
The Happy Valley Zone is a Zone on Mobius. The area was only briefly seen at Christmas, with Doctor Robotnik furious that the citizens were enjoying themselves without his permission. To enact his revenge, Robotnik planned to fire his new Egg Satellite at the Zone, heating up all the snow so that it would melt, creating floods that would wash away all their homes. Fortunately, Robotnik was stopped from pressing the button by an appearance from Father Christmas. While the tyrant was distracted, Shortfuse the Cybernik destroyed the weapon and saved Christmas for all residents for the Happy Valley Zone.