It all depends on which game wewe have... I remember that to get to level 31 in crash Bandicoot 3: Warped, wewe need to get caught kwa the sekunde Pteridactyl in the group of them near the end of level four. I'm not certain of this, so wewe should check it just in case.
I've got two: -Crash Bandicoot:Warped, on one of the motorcycle levels there is a yellow sign with an alien face on it. Crash the bike into it and wewe will be transported to a secret level wewe can't access anywhere else -In Crash Bandicoot:The Wrath of Cortex, start a new profaili and type your name to be 'Wombat'. When the cutscene finishes, wewe will have unlocked everything, even the secret platform in the middle. That's all I know.