Mexico opens windows on buried treasures\

Archaeologists in Mexico City announced plans Friday to hold tours of inaccessible buried ruins via glass-covered shafts looking down on the sites.

Two daylong guided tours of the sites, known as "archaeological windows," are scheduled for April, and will take visitors to about 20 sites currently open to the public, as well as 20 more "windows" hidden beneath stairwells, floors and patios of buildings normally not open to the public.

The underground ruins — some swallowed or encased by the foundations of the Spanish buildings constructed atop them following the 1521 conquest — cannot be fully excavated without destroying the crumbling colonial buildings above them.