I actually managed to somehow get Spyro out of the bounds of the level, come back, leap off the castle roofs and go as high as possible - And there really is..... Nothing except the return portal. Found some pretty funny glitches though xD

But there is a small opening in the invisible wall where you can go through.
I didn't find any secret portal or level, just something that could probably be called a skateboard proxy jump.

One possibility is that someone fell down through the hole and got close to the area exit without knowing and thought it was a secret level.

Has anyone actually seen this 'hidden world'? Because I'm pretty certain it's fake now.

For those who haven't heard of it: In the Enchanted Towers Skate Park, skate up the portal you come through via the rocks & grass, and apparently there's a secret level.