Royal Palace

With 3,418 rooms, the Royal Palace of Madrid is the largest royal palace in Europe — bigger than Buckingham Palace, bigger than Versailles in sheer room count. The Spanish royal family hasn't actually lived here since Alfonso XIII left in 1931, but it remains the official residence of the monarchy, and King Felipe VI still uses it for state ceremonies. It's a working palace that nobody sleeps in.

The current building rose from ashes — literally. The old Alcazar, a medieval Moorish fortress expanded by the Habsburgs, burned to the ground on Christmas Eve 1734. Philip V, who'd grown up at Versailles and never much liked the drafty old castle, saw the fire as an opportunity. He ordered an entirely new palace in the Italian Baroque style, insisting it be built entirely of stone and brick so it could never burn again. Construction started in 1738 under architect Filippo Juvara, continued under Giovanni Battista Sacchetti after Juvara's death, and wasn't finished until 1764 under Charles III, who became the first king to live in it.

Inside, the opulence is staggering. The Throne Room drips with Tiepolo ceiling frescoes. The Royal Pharmacy still displays centuries-old apothecary jars. And the Royal Armoury preserves one of the world's finest collections of arms and armor, including the personal gear of Charles V and Philip II. But the palace's most extraordinary possession might be the Stradivarius Quartet — actually a quintet — the only complete set of Stradivarius string instruments in the world, all built by Antonio Stradivari between 1696 and 1709.

The gardens of Campo del Moro behind the palace stretch down to the Manzanares River, offering one of the best views of the building's western facade — a perspective most visitors miss entirely.