What is the deepest valley in the world?
Kali Gandaki Gorge
The Kali Gandaki Gorge or Andha Galchi is the gorge of the Kali Gandaki (or Gandaki River) in the Himalayas in Nepal. The Kali Gandaki gorge is the deepest gorge in the world, being 24,071ft or 7,337m lower than Annapurna I which bounds it at one point.
Blauhöhle
The Blauhöhle is the largest cave system in the Swabian Alps in southern Germany. The Blauhöhle presumably originated in a time when the Danube still flowed through the Blau valley. Since the shifting of the Danube, several small rivers, the Schmiech, the Ach, and the Blau, have flowed through this valley. The cave system begins about 21 meters under water at the base of the Blautopf. It continues west and northwest, rising and falling several times until after a horizontal distance of about it comes above the level of ground water and opens into the second big air-filled chamber. The maximum depth of the cave under water is .