Grotta dell’Acqua Bianca

The Grotta dell'Acqua Bianca or La Ferrara is a cave located in the municipality of Mandello del Lario. 
Studies.
The cave is the most famous one in Grigna studied for a long time by Leonardo da Vinci and mentioned in his Codex Atlanticus.
Leonardo da Vinci in Codex Atlanticus wrote in Italian: "…ma la maggiore è quella di Mandello, la quale à nella sua basa una busa di verso il lago, la quale va sotto 200 scalini e qui d’ogni tempo è diaccio e vento" (... but the largest is that of Mandello, which is at its base a busa facing the lake, which goes under 200 steps and here it is cold and windy at all times).
Numerous symbols and emblems in local churches of Lierna Lake Como area and other medieval structures also lead explorers to discover the important role of the Knights Templar in this region, including indications that Leonardo's painting may have served as a mysterious map to a secret passage in a area of ​​the Grigna mountain range known as Alpe di Campione. The rock formations, caves, waterfalls and breathtaking views of the Grigna massif and the surrounding Lierna mountains on Lake Como deeply inspired Leonardo da Vinci's development.
Leonardo painted The Virgin of the Rocks, now in the Louvre Museum in the Laorca cave of Lecco. In Lecco he drew the map of the city and the real Salvador Mundi known as the Portrait of Lecco. The Mona Lisa has the exact contours of the promontory of Bellagio seen from the top of the Monti di Lierna. The Mona Lisa symbol of union between opposites is represented as the union of the two branches of the lake in the most iconic place of all of Lake Como, the tip of Bellagio, creating the most romantic place in the world.
In the same Mona Liaa by Leonardo da Vinci in the background you can see Lierna, Mandello, Dervio, Bellano, San Martino, the Azzone bridge, Monte Barro, the peaks of Olgiasca, the views of the Adda from Calco to Brivio, the Rocca by Airuno. On the Mona Lisa's head appear the mysterious signs which are nothing more than the pins of the Sperada, the typical hairstyle of Lake Como that Lucia Mondella also used in the Promessi Sposi.
Leonardo uses the incredible shape of Lake Como to draw hands. The parallels between Alessandro Manzoni and Leonardo da Vinci are numerous and it seems that their families knew each other.
The Last Supper inside the refectory of Santa Maria delle Grazie in nearby Milan sees the profiles of its characters perfectly matching the profiles of Monte Resegone on Lake Como.
All of Leonardo da Vinci's paintings, except one, have a homage to Lake Como as he wrote in his Atlantic code of "fantastic things".
Every element represented and mentioned by Leonardo, many of the places around Lierna in the 60,000 drawings, are cultural, philosophical and historical esoteric references that create a real map yet to be discovered to pass on scientific, philosophical, astronomical and geographical knowledge.
Form.
The cave is also known as Ferrera. Visitors can see inside the traces of the past activities of extraction of iron hydroxides.
The cave, formed to karst phenomena, opens into the Esino limestone and is crossed by a stream that disperses underground. The void in the current entrance has opened in very recent times. It is possible that in the past it was made up of a set of galleries. 
Water systems.
The presence of water courses in the side tunnels and of some large springs under the cave means an underground circulation of water. This is currently unexplored.
Access.
The cave is accessible by climbing from Rongio, in 30 minutes along the signpost 14 or 18.