Externica: Okay, I tried it for hours now and I'm too blind to solve this.
I'm at the very beginning, I activate the moving platform with the spin and go to the lower level. All right.
Then, after activating the save point on the lower half I'm stuck.
Above the save spot is another switch. I can't reach it. Going further to the right brings me to a small "cliff", but even there I'm stuck after a while, as I need to activate the second moving plattform with the switch above the save spot.
I swam through the water bassin and can't, but I can't see a hidden passage or something similar.
So obviously, I'm missing some vital clue.
So you have taken the platform down and there is a brick wall in font of you, water below you and a switch above you?
You dash through the brick wall and need to get up to the switch.
Jump up and then dash straight upwards as punk Giana. That will clear the height you need to reach teh switch.
(just ran through that bit again to check)
Edit:
By the way. This is in my opinion the most stupid evel in the game and the last stretch will make you want to kill the level designer and at the very least through your digital download out the window. If you had a physical copy of the game it would be in real danger of being broken in frustration...