Lights glitter on the night skyline as you spring from level to level. Race through corridors, then jump on top and grab those Rings!
— Description from the Master System manual.
Gigalopolis Zone (ギガロポリス Gigaroporisu?, lit. "Gigalopolis"), shortened to Gigapolis Zone on the level title cards of the international Game Gear version, is the second Zone of Sonic Chaos for the Master System and Game Gear. In keeping with the other stages of this game, Gigalopolis consists of two standard Acts followed by a shorter, third Act which contains the Zone's boss. Gigalopolis Zone follows Turquoise Hill Zone and precedes Sleeping Egg Zone.
Gigalopolis Zone (shortened Gigapolis Zone in the Game Gear port except in Japan) sees Sonic run through an urban environment at night, under the stars. Some of the level resembles a construction site, with orange, metal frameworks and seemingly incomplete block walls. The background displays various high-rise buildings as well. Taken together, these features are somewhat reminiscent of Star Light Zone from the 16-bit Sonic the Hedgehog; and since both these games take place on South Island, it would not be unreasonable to speculate that the two zones are close neighbors.
Gigalopolis Zone's boss is some sort of giant, upright, mechanical caterpillar. The machine attacks by lobbing the spherical segments of its own body in Sonic or Tails's direction. Dodge the metal balls and hit the automaton on its glass-shielded cranium to defeat it.