Having already delved into the secrets of the ancient world in their 2015 documentary Rome’s Invisible City, Alexander Armstrong and Dr Michael Scott return with a three-part series that takes them further afield, visiting Venice, Florence and, in this first programme, Naples.

They begin in the city centre,  exploring a tunnel network that links historic quarries and Roman aqueducts and is home to an abandoned metro line.

The adventurers also visit Herculaneum, where an underground theatre was buried after Vesuvius erupted, and venture underwater to explore Baiae’s sunken harbour, Portus Julius.