The Etruscans were skilled engineers and plumbers and, in Formello, you can visit some of their accomplishments. Today these tunnels are more for nature tourism and archeology, but the place has feelings that make it worth a visit. The Ponte Sodo tunnel was excavated by the Etruscans to drain the water of the river during floods of the Cremera lest it inundate the Veii flatlands. Here you can see an internal cascading river whose waters are reflected with a thousand colours from the rocks and vegetation in it.
Meanwhile the three tunnels of the trench aqueduct of the Olmetti were dug to control the waters of that area. The tunnels have amazing reflections and are isolated from the rest of the world as if they were tropical ruins.