Puerta del Sol

Stand on the small bronze plaque in the pavement here and you're standing at the exact center of Spain. Kilometer Zero — the point from which every radial road in the country is measured — sits right at your feet, embedded in the sidewalk in front of the old post office building. Every distance marker on every highway in Spain counts from this spot. It's the belly button of a nation, and most people walk right over it without looking down.

The name means "Gate of the Sun," after a gate in the 15th-century city wall that faced east toward the sunrise. The gate is long gone, demolished centuries ago, but the name stuck. The crescent-shaped square you see today took its current form between 1857 and 1862, when the government bulldozed a clutch of medieval buildings to create a grand civic space. The old post office — now the regional government headquarters — was built even earlier, between 1766 and 1768, by French architect Jacques Marquet, and its clock tower has become the emotional center of Spain's New Year celebrations.

Every December 31st, millions of Spaniards watch those clock hands on television, stuffing twelve grapes into their mouths — one per chime at midnight. Get them all down in time and you'll have good luck for the year. It's harder than it sounds, and the square fills with tens of thousands of people attempting the feat together, cheeks bulging, champagne at the ready.

This is also where modern Spanish protest was reborn. In May 2011, the 15-M movement — Spain's version of Occupy — turned Puerta del Sol into a tent city for weeks, with thousands camping out against austerity measures. The square has always been where Madrid comes to celebrate, mourn, and demand change.