The architectural complexity of Amsterdam is causing engineers to use innovative new techniques in the bid to provide the city with a subway system.
Plans for the $2.4 billion project began in 2003, with completion scheduled for 2013 - but a number of obstacles have sprung up along the way.
Johan Bosch, project manager, told the Associated Press that some 7,000 mirrors had recently been hung along the 2.4 mile length of the underground route, so as to establish any whether the city's watery foundations cause any sections of building to shift.
"The politicians told us: 'We want a subway, we're prepared to pay for it and accept some disruption, but the one thing we absolutely don't want is any damage to the city'," he said. "We need a system so that if things don't go as expected, we don't find out after the damage is irreparable.
"We now know that whole segments of the city move by themselves, a number of millimeters over the course of a season," he added.
The workers are beset by other difficulties, including continuing construction underneath the city's Central Station without disturbing its 250,000 daily passengers, as well as having to use decompression chambers to avoid 'the bends' when digging tunnels below sea level.
