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 the player 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.
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 the player until it is almost defeated. Then it will jump off-screen at a very high altitude and will land at the player. If the player dodges it, he/she must also jump to avoid taking damage from the shaking ground the impact of the landing causes. It will then bounce around again and off screen every once in a while until defeated.