Some weeks ago a friend of mine and me went to the Gleinker See (next to Roßleithen) in Upper Austria.
We also walked to the “Piessling Ursprung”, a water source that can give water to 100.000 people in Upper Austria on summerdays. The turquoise pothole is around 32 meters deep, before a cave is popping up. Around 1500 meters of the cave were explored before there was a diving accident. Now the cave is closed for diving. The deepest explored area is around 80m deep.
The walk there is really easy, you are walking on an asphalt street next to houses – around an hour from the Gleinker lake.