Another building that we will see in Puerta del Sol, is the Real Casa de Correos (Royal Post Office Building), built in the late eighteenth century, which makes it the oldest building in Sol.
In the tower we see in the photograph above, is the famous and very televised clock, the star of the show, every midnight December 31st, when it gives us the bell tones for the twelve seconds after midnight so lots of people worldwide will take the 12 grapes for next year wishes.
This building was built with an ambivalence in mind, postal services, and for citizen security and supervision.
In 1847, it the building was reorganized inside, to make it into the Ministry of Interior, and leaving the ground floor, as a post office. Until the early twentieth century, people could still deposit letters in the mailboxes with the form of lion heads, that still existed on the side of this building facing Carretas street.
Puerta del Sol is a square of Madrid that since 1950 is considered as the Kilometer Zero of Spain. From here, all the radial network of Spanish roads start counting distances.
Also, the numbers of buildings in streets of Madrid, have their lowest numbering, at the closest point to the KM 0 point of Puerta del Sol.
This KM O is marked on the sidewalk, just below the clock in the picture.