Plato’s Cave is the only cave in Italy that is still being explored.
The cave is one of the oldest of its kind in the world, dating back to at least the second century BCE.
It is situated at the mouth of the Tiber River in the province of Verona.
The waterway was once the main route for trade between the Mediterranean and Asia.
The lake is located in the south of the Italian state, between Venice and Naples.
It was once a major port for ships and trading.
There are currently more than 1,500 people living in the cave, which was originally inhabited by people from all over the Mediterranean world.
Italian President Sergio Mattarella said the project had been a long and difficult one, and was now finished.
“We are not finished yet.
This is a great success story for the country and for the project,” Mattarella told reporters on Thursday.
The cave is located on the shores of the Mediterranean Sea, a part of Italy where water is shallow and there are no rivers.
It lies about 3 kilometres (1.8 miles) from the village of Verdo, where a new tourism centre is to open next year.
The project, which will be named after the Greek philosopher, was initially set up to preserve a part a Roman road from Verdo to the Colosseum.
The original plan was to preserve the ancient walls and ceilings of the cave.
But the original plan for the cave was scrapped in the 1960s because of a lack of funds.
The only way to protect the cave from erosion and other natural processes was to create a temporary shelter.
However, it took nearly two decades for the temporary shelter to be built and the cave to be opened.
This article first appeared on BBC World Service.