"The issue is not the metro itself, which is going to run far enough below the surface that there is no risk," said Giovanni Simonacci, the Metro C project's technical director.
The problem, he said, is figuring out how to get people from the surface of the city down to the metro line without disturbing an important historic structure.
"We don't know where (the precise entry and exit points) will be yet because we don't know what is down there," he said.
Not just a recent pheneomenon either as Seattle's underground attests.
Actually, my first encounter with the Seattle Underground was from the pilot movie to Kolchak: The Night Stalker. The reality is sadly disappointing.