The Ferriera ( o Ferrera ), named also Cave of Copper or Acqua Bianca Cave in Mandello del Lario , is one of the most known caves of Grigna, outside of speleology world.
The cave , formed by karst phenomena and composed by Limestone of Esino , is criss-crossed by one creek that disperses in the underground. The void that you can find in the current entrancy has recentrly opened , it is possible that in the past it was composed by a combination of galleries. The presence of water courses in the lateral tunnels and of big water sources (like the Acqua Bianca one ) under the cave are testimonies of underground circulation of water , but unfortunately it cannot be explored.
The cave is reachable from Rongio , in 30 minutes following the trail way 14 or 18.
We are grateful to CAI Grigne – Mandello del Lario section for the information and the pictures , for more details go to the website : www.caigrigne.it