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.
A part of the cave-system was opened to the public in 1974 with many improvements in safety for the visitors in later years. At one point colored lights found their way in with some spectacular and dramatic effects.
My photos inside the cave are in the wrong order, not sure how to interchange them or what I've done wrong when uploading, sorry!