 Complete the following phrase:  It measures 72 by 68 metres, with a height of 23 metres, and occupies an area of 4,828 square metres. It is constructed on the side of a hill and two of its sides are surrounded by elevations. There are no ornamental facets on the exterior, except for a few windows at the top of each storage room. It has cornices built in a Doric style, constructed with two types of regional stonereddish and greenish. This gives it a curious appearance, resembling a stronghold or a castle, which it has come to be called by the people of Guanajuato. In the interior, there is a porch that leads to a spacious central patio. The porch contains Tuscan columns and adornments. There are two staircases that lead to the upper floor. The Grain Exchange building has only two access doors, a small one facing the east, adorned by two columns, and a large door of the same basic style, facing the north. The edifice was used for the buying and selling of wheat, corn, and other grains. Prior to the 