Page last updated at 07:21 GMT, Saturday, 2 May 2009 08:21 UK
The 'underground world' of Naples
A new research project has begun into the caves that lie below the Italian city of Naples. More than 900 have been discovered so far, but that is believed to be only a third of what actually lies below.
The caves have been dug out over thousands of years and used for everything from aqueducts to air raid shelters.
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