I humbly confess that there's not a single flag in 'Eurydice'. This was my second level; I didn't start using flags (or COs, for that matter) until some time afterwards. Too much voodoo for my limited know-how.
I spent 3 years working in Quality Assirance for a video game developer
so sorry if I come across as opinionated
but I wanted to tell you how much FUN I have had playing this level!
That is, until I got to this part. I CAN'T get past it.
Man, you had me terrified with the 'opinionated' line; never before has that preceded good news!
It is really really great to get feedback, especially after all this time since I released this level, and from someone with your job! So thanks a ton for saying you're enjoying it! I had a lot of fun working on this level back in the day, and I'm glad it's still being played and is fun.
As chance would have it, I played through this level for the first time in maybe a year a couple of weeks ago, and discovered a variety of little points that I found borderline-frustrating; maybe I will release a new addition some day soon - wish I'd taken notes as I played through it now.
Sorry about the particular thing that's got you stuck now, though; I distinctly remember making and testing that part, and even remember that I only made the spikes cover the whole ceiling because it was more aesthetically pleasing than if they stopped part-way.
As for an immediate solution, I have three suggestions.
1. If you're not already, try playing the section in full-screen. You can full-screen-ify KS by pressing alt+enter. I think it's more than placebo that that does make some jumps and tricks easier; it might make jumping out of there possible.
2. Edit the screen using the level editor. (Assuming you know nothing about how the editor works) Open 'Eurydice' in the KS level editor, navigate to screen 1034,1027, press '5' on your keyboard and then left-click and run the mouse pointer over the spikes above the switch; the red boxes covering the spikes should disappear - the red boxes are what kills you; the spikes themselves are just graphics. Save and then go back to the level - you can resume your saved game without any problems.
3. Use the Top Secret KS Cheat; type 'Knytt Stories cheat' into youtube and watch the magic happen. I don't really recommend this because I find that once you start using the cheat, it's really had to stop (cf. Dark Sea 2).
Anyway, I'm really glad you're having fun, thanks for commenting to say as much, I hope you can make it past those spikes and I'm really, really sorry about the pitch-dark screens near the end. If'n'when you get to the end, I'd love to hear your full opinion. Also, if you haven't already tried out my other levels, they're posted in my signature (sorry, that was a shameless plug).