Use stone near, at left for exaple. Must be big one. It's little difficult, but works. I checked. Press "flap and down" many times.

That worked for me but now im trapped inside the cave in the screenshot. There was another big stone inside but i didn't make it out on my first attempt and now I can't dive down far enough to get out.

Kishgla, try to use instruction from user manuals.

\Steam\SteamApps\common\Secrets of Raetikon\save\sync\master\user.progress.xml

playerPosition="-21.641996 -186.618607"

Edit #2 for up.

Hey! This spot is a bit evil, but you do get out of there even without a rock or hacking the savegame! Do as described:

• Fly as close to the ceiling as possible
  
• Don't stay too close to the wall on the left, make sure you're looking to the left side
  
• Do a nosedive, then press the flap button and keep both pressed the entire time. This way your bird will flap underwater in the optimal timing.
  
• If you started in the right spot, this move should make you dive out in exactly the right angle!

As I said, this spot is a bit evil as you can easily get trapped, seemingly w/o a way out. We might change this in a update sometime.