To the south of Puerta del Sol stands the iconic Old Post Building, the oldest in the square, red and white, shaped like a majestic palace. The old postal building was built by French architect Jacques Marquet from 1766 to 1768, and the bell tower on the top was added in 1867. Every New Year's Eve, Madrid people gather here to celebrate the arrival of the New Year by eating 12 grapes symbolizing good luck when the sound of midnight. It is a tourist attraction that tourists will not ignore, and the crowd is dense. On the side of the square in front of the building, there is a 1-foot-diameter ring inside the ring with a map of the Iberian Peninsula, with the words "zero kilometers" in the center of the map. Spain uses "zero kilometers" as the starting point, and the milestones of the national highway are calculated outwards from here. Plaza del Sol is also the starting point of the Madrid city's house number.