UNESCO sites face major obstacles

A number of UNESCO's World Heritage Sites face major challenges, including the following:

Machu Picchu, Peru

This magnificent "lost city of the Incas" is cited by UNESCO as beset by logging, poor waste management and agricultural incursion but hasn't been placed on its list of sites in danger. Peruvian experts are raising other alarm bells, from vehicle fumes to the unceasing tread of footsteps producing a similar effect as a small-scale earthquake that could lead to the collapse of the temples and other structures.