There's no cheat code, Action Replay sequence, or hidden menu to instantly unlock every Friend Area in Pokémon Mystery Dungeon: Red Rescue Team. They're earned exclusively through normal gameplay progression. Here's how to get them all legitimately.
Using a cheat device to force-unlock Friend Areas risks corrupting your save file, breaking script triggers, or flagging your file as modified (which matters if you ever trade Pokémon or use online features via emulation). More importantly, Mystery Dungeon is designed around the satisfaction of gradually building your rescue team's base. Unlocking areas organically ties directly to the game's core loop: explore, rescue, expand, repeat.
Enjoy the journey. The sense of accomplishment when you finally recruit that elusive Legendary into its custom Friend Area is the whole point.