I've only known about this level for a year or so, since somebody mentioned it on my channel. I don't know why, but I never bothered to search for a way to play it, or even find out if you could play it. Then jbreckmckye posted a video of it today and he was kind enough to include the code and explain how to play it. Obviously, I had to try it and I had to get the gem on it.
I must say this is the hardest and quite possibly the best Crash Bandicoot level ever. It's a shame they left it out of the game, as it only would have made an already excellent game better. Yeah, it's hard, but it's not that hard to beat normally. After all, there are three checkpoints here, contrary to Slippery Climb, which only has one. Getting the gem, however, is a nightmare, and I needed close to 50 attempts.
There are three invisible tokens (probably Tawna) on this level, but the bonus stage it unlocks doesn't exist, so getting all three will crash the game. You can see it in jbreckmckye's video. So, in order to get the gem, you have to avoid getting one of these. Location of tokens: 0:27, 3:21 and 4:48. I didn't get the first one.
How to play the level? I'll just copy the info from jbreckmckye's video.
ACCESSING "STORMY ASCENT"
You need to use one of the following codes, depending on the version you have:
AMERICAN VERSION:
D0011DB2 3404
80011DB0 0022
EUROPEAN VERSION:
D0011DD2 3404
80011DD0 0022
JAPANESE VERSION:
D0011DFA 3404
80011DF8 0022
You need to enter these codes, make them active, and then boot the game up. You can't just turn them on whilst the game is running - you need to activate the GameShark, and then reset the console / emulator. Done correctly, you'll see the standard piracy screen and then, instead of the 'Universal Studios production' logo, you'll just see the loading screen for Stormy Ascent.