This is why almost everyone visits León—to see the sun shine through the most dramatic stained glass windows in Spain. There are 125 in all (plus 57 oculi), dating from the 13th century. They are so heavy that the roof of the cathedral is held up not by the walls, but by flying buttresses. In the church-building frenzy of the Middle Ages, every Gothic cathedral vied to distinguish itself with some superlative trait. Milan Cathedral was the biggest, Chartres had the most inspiring stained-glass windows, Palma de Mallorca had the largest rose window, and so on. Structurally, though, the boldest cathedral was at León. This edifice set a record for the greatest proportion of window space, with stained-glass windows soaring 34m (112 ft.) to the vaulted ceiling, framed by the slenderest of columns. The windows occupy 1,672 sq. m (nearly 18,000 sq. ft.), or almost all the space where you’d expect the walls to be. Inside, the profusion of light and the illusion of weightlessness astonish even medievalists. The architects (Juan Pérez and Maestro Enrique) who designed the cathedral in the 13th century were, in effect, precursors of architect Mies van der Rohe, 7 centuries before the age of steel girders draped with plate-glass curtain walls. It is the experience of being surrounded by color and light that makes this cathedral so special.