Puerta del Sol

The Puerta del Sol (Spanish for “Gate of the Sun”) is a public square in Madrid, one of the best known and busiest places in the city. This is the centre (Km 0) of the radial network of Spanish roads. The square also contains the famous clock whose bells mark the traditional eating of the Twelve Grapes and the beginning of a new year. The New Year’s celebration has been broadcast live on national television since 31 December 1962.
The Puerta is located in the very heart of Madrid. It serves as the kilometre zero from which all radial roads in Spain are measured. This is demonstrated by a plaque on the floor of the square, marking the exact point of Km.0. The old plaque was replaced in 2009, after the old one had become faded after years of foot traffic. It is also the reference for street numbers in Madrid, which begin at the street-end that is closest to Puerta del Sol.
Immediately to the southwest lies the Plaza Mayor; the Palacio Real, the official home of the Royal Family, is further west. Parliament and the museum district are to the east and the train station Atocha is to the southeast.
Source : Wikipedia 
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