Just off Piazza Tasso, the main square in Sorrento, is a surprise. There is a deep ravine which holds a group of old mills, now abandoned.
From the top only a couple of buildings are visible, but there are 25 in total. They were flour mills and saw mills, powered by water from fast flowing streams. Some date from the 13th century. They were abandoned in the early 20th century and are now disappearing in the undergrowth.
You can see how deep the ravine is in this photo.
I think it is possible to walk through the area, but I am not sure how to do so. There is a track from the top, but it has collapsed in a couple of places. There must be another entrance. I will investigate on my next visit to Sorrento.