The 

The Puerta del Sol symbolizes for Madrid the center as a meeting point. Many subway lines converge there, and there is a large retail concentration, so these days people flock there for a stroll and (a few) for shopping. It is also the place to receive the new year, as Times square is in New York; in the photo under this lines, to the left you will see the clock to whose bell spaniards swallow 12 grapes when the new year arrives (one of these deliciously absurd traditions that, in the end, define a country through the memories of its people).

Happy Christmas!