Although its name includes the denomination of "puerta" (gate), in fact it's a square, the true nerve center of Madrid. From here start several of the most important streets, such as Alcalá, Mayor, Arenal or Preciados, and the main roads of Spain. You will have to put your feet on the Kilometer 0 or make a selfie next to the statue of the Bear and the Madroño as proof that you have been here.