Monumental Challenge

More than 150 years old, it's the world's most famous clock - but with problems ranging from an aging mechanism and constant attack from pigeons, to surface-destroying pollutants and a weakening foundation, will England's Big Ben make it to the next century? Cared for by a handful of professionals, including metal workers, glazers, and three wise men who ensure the clock runs smoothly, it is a daily struggle to keep the clock upright and on time.

Visited by more than seven million people a year, the Eiffel Tower in Paris is facing one of the most challenging periods in its history. Its ambitious regeneration plan includes a hydraulic lift, a paint job, and meeting critical new energy-saving targets - not to mention the fact that many of its 300-strong maintenance crew are required to perform much of this work while hanging from the tower.

With the Yamuna River as both a backdrop to the world's most famous monument to love, and its greatest threat, the workers at the Taj Mahal face constant challenges on a daily basis. But with the Commonwealth Games looming these challenges just got even harder. They must restore sandstone archways, clean the famed blue-veined marble safely and replant much of the gardens. All, while they race against the clock.

A financial hub in China undergoes a transformation with the addition of a waterfront, parks and a new transportation system.