Crash Bandicoot - Waterfall level
This is one of a few lost levels that were scrapped early in development. They're all unnamed and unfinished, featuring themes, enemies, and mechanics not seen in the final game at all, as well as lacking crates and pick-ups. They were cut very early on, so even though they're still in the prototype's code, the only way to access them is with a hack.
It's a mostly vertical level in side-scrolling fashion.