But there is a place within the Vatican that's rarely seen. Hidden beneath the city is an underground fortress. Inaccessible to the public and protected by armed guards and state-of-the-art security.

Aerial view of Rome and Vatican from police helicopter patrol. The body of the 88-year-old pope, who died on Monday in his rooms at the Vatican's Santa Marta guesthouse after suffering a stroke, ...

Its massive walls, topped by stone eagles and statues of saints, dwarf the crowds of tourists queuing to see the treasures inside its museums. The Vatican may look like a medieval fortress, but ...