Under the 316ha Olympic central area where the "Bird's Nest" and several other major Olympic projects are located, a 9.8km path is being constructed to link the venues and ease ground traffic congestion.

The tunnel, 12.6m wide and 12-17m below the earth surface, is designed to have outlets to the National Stadium (the "Bird's Nest",) the National Aquatics Center (the "Water Cube",) the National Indoor Stadium, the National Convention Center, the Digital Beijing Building, the Olympic Village, the China Science and Technology Museum and others.

At the same time, a 40,000 sq m two-story underground parking project is being built to contain some 1,000 cars. Solar energy is being introduced to light the parking facility.

The third underground project is a subsided square nearby the National Convention Center, which is divided into seven yards featuring the red walls of the Forbidden City, typical Beijing courtyard houses, traditional Chinese musical instruments like the drums, and the sport sites including the polo grounds, local newspaper the First quoted a source of XinAo Group as saying.

"A new look combining the elements of an open Forbidden City and the courthouses along the city's central axis and amid the modern Olympic projects gives the viewers food for thought," said the source, who brought the press's attention to the objects visible from the ground level.

For the sake of environmental protection, energy-saving and quality construction of the underground projects, a kind of "bubble mixed light soil" and the steel slag of Shougang Group were chosen instead of cement as the building material for their roof and they proved to be lighter, durable and cheaper, it was reported.