If you ever stay in the south of Spain in Andalusia, I highly recommend the Caminito del Rey.
It's a gap that you can only visit with a guide.
There is a wooden path about 100 meters above the river El Chorro. It's attached to the rock face and barely a metre wide. It connects two hydraulic power stations at the waterfalls along both sides of the gorge.
On the right you will see the hiking trail that is attached to the gaping wall. It offers spectacular views: beautiful rocks, formed in a very distant past, when the sea stood more than 100 meters higher. (You see: the sea level rises not only because of the stupidity of man, many years ago the water also rose well above our lips...)
We know that because there are fossils of marine animals at more than a hundred meters altitude, where you walk. They are depicted forever, trapped in stone.
For example, in the Cevennes, in the south of France, I already saw prints of dinosaur spots and last week, during a walk in my own village, this print of a perished leaf in the walkway of barely one and a half years old.