MEXICO CITY: Archaeologists here are planning tours of otherwise inaccessible, buried ruins through glass-covered shafts looking down on the sites.

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

Among the sites shown in an initial tour is an Aztec "quincunce" stone discovered about three decades ago beneath the city's cathedral. The origins of the archaeological window technique go back to the early 1900s, when archaeologists began burrowing down to Aztec temples without disturbing the Baroque structures above them. By the 1960s, as subway lines were sunk through the downtown area, Aztec temples began turning up and being preserved even in subway stations.

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