Il Pertus (Colombano Romean Tunnel)

The Pertus is a tunnel that can be walked on a hiking level, provided that:
You have waterproof shoes as you walk on the surface of the water of a countercurrent stream that flows inside.
You do not suffer from claustrophobia and have a torch as it is completely dark and narrow in places.
Be fairly covered as the temperature inside drops considerably.
The Pertus can be walked in about 40 minutes, or simply look at it from the outside and then climb to the 4-teeth peak.

A tunnel driven 500m through the mountain by this miner and stonecutter Colombano Romean, which directs the water of the Rio Thullie on the "right" side. 1526-1534. A man. 500m. Just imagine that.

At low tide, with a torch and appropriate shoes, you can venture into it a little (completely?).