This level was present in the original version of the game, but was removed before its release, as it was considered too difficult. It was the last level before the final battle and has been replaced with the fictitious level The Great Hall, which is actually only for seeing the alternate ending after finding all the gems. It can however be played using a GameShark code. Stormy Ascent was later reintroduced in the N. Sane Trilogy, where it is the thirtieth level of the game, including boss fights.
Stormy Ascent is essentially a harder version of Slippery Climb, already thought by many to be the hardest level in the game. A side-scrolling level filled with pitfalls and moving platforms, where it's very easy to fall into the void. The platforms move even faster and weirder than in the previous level, so you need perfect timing to proceed. There are even more scientists throwing explosive vials, and some elements typical of other levels also appear, such as rotating bridges. Just before the exit portal there is an extremely difficult obstacle to overcome, having to jump on three vultures that move sideways.
There is a Nitrus Brio bonus level, playable only in the N. Sane trilogy.