After many devastating battles between the Knights and Turkish armies, Valletta was established as the island’s new capital and its defences were expanded deep under its streets.
Not only did the Knights build a sophisticated sewer system but they carved out food and water caches under the city, ensuring access to vital resources should Valletta ever fall under siege.
And once the work was done, the residents of Valletta took up their own pickaxes and continued to burrow deep underground.
They built dwellings and businesses and came to be known as the “children of the underground”.
Architect Mark Zimmerman of Underground Malta said: “Overall, Malta’s underground world is really very extensive and fascinating.
“It is a literal Swiss cheese down here.