Crash Bandicoot/Slippery Climb

Probably the hardest level in the game. It's a side scrolling level, where you have to climb the castle facade using moving platforms, disappearing ladders, and even some vultures. You'll also need to avoid spikes and hands trying to grab you, as well as defeating scientists who throw explosive vials at you. What makes this level so difficult is the lack of C boxes: there is in fact only one, exactly in the middle. However, if you manage to pass this level without losing lives, you will be awarded the red gem.

A curiosity: in the original version of the game, this level also had a more difficult twin: Stormy Ascent. It was the last level before the final fight and was later canceled due to its excessive difficulty.