While this was my second visit, I've enjoyed it as much as the first one!
The first gallery of this system of caves was discovered by locals in 1947. Of course people were curious and had to investigate further. What is known today is that the cave reaches 11 Kilometers in length which makes it the biggest and most important in Portugal. The formation of the cave goes back 150 million years to the middle Jurassic age when dinosaurs inhabited this region. They found traces of species who inhabited these caves, some of it on display.