Secret Base Zone is the second level of Sonic Advance for the GameBoy Advance. A typical factory 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, free-floating iron platforms... Less usual gimmicks include ziplines criss-crossing 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.
- Mogu - Mole badnik that pops out of the ground.
- Tentou - Moth badnik that shoots energy balls.
- Senbon - Pufferfish badnik.