Men in coveralls, chest-high waders, thick industrial gloves and goggles are harnessed up and descend a ladder into the sewer, watched by figures with oxygen tanks strapped to their backs.

One team member must wait while the rest descend a ladder and dig out a buried flag.

Descending the ladder and taking that first symbolic step was not the most significant part.

As the group descended a ladder through the secret passage, another aftershock shook the ladder off.