Secret Base Zone is the second zone of Sonic Advance for the Game Boy Advance. A typical factory-city installation of the Eggman Empire, this industrial setting features a host of manufacturing-based obstacles: swinging hooks to leap across the ceiling, pressurized tubes to sweep you through a pipe network, steam tops, lava crucibles, and free-floating iron platforms. Less usual gimmicks include zip-lines crisscrossing the foreground, and dual chutes that drop the player through the background.
Many of the features in this level first debuted in Metropolis Zone from Sonic the Hedgehog 2. A unique effect in the very first, outdoor part of Act 1 is an interesting floodlight motif, later used in Sonic Advance 2's Ice Paradise Zone. At the end of act 2, Sonic battles Eggman in a pogo-like Egg Mobile. It will bounce around trying to hit you until it is almost defeated. Then it will jump off screen and will land were ever you are. If you do dodge it you must also jump to avoid taking damage from the shaking ground. It will then bounce around again and off screen every once in a while until defeated.