 The first church built on the cathedral site also had a tabernacle , but its exact location is unknown . During the construction of the cathedral , the tabernacle was housed in what are now the Chapels of San Isidro and Our Lady of <unk> of Granada . However , in the 18th century , it was decided to build a structure that was separate , but still connected , to the main cathedral . It is constructed of tezontle ( a reddish porous volcanic rock ) and white stone in the shape of a Greek cross with its southern facade faces the <unk> . It is connected to the main cathedral via the Chapel of San Isidro . 
