This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

The eclectic observatory castle of a 19th-century astronomer and explorer.

The water swaps direction twice a day, whipping into a frenzy of whirlpools and rapids.

The Incas turned this ancient Wari aqueduct into an imposing defensive gate.

A rare example of World War I trenches from the British front.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

A backdoor to Machu Picchu that only the most foolhardy infiltrator would attempt to breach.

The island residents are known for taking their quirky sense of humor with them to the grave.

The tower claims to be the world's only pagoda made entirely from Myanmar's lucrative gemstone.

Abandoned blockhouses from Nazi Germany's Atlantic Wall erode into the sea on a French beach.

Visiting dignitaries and Hollywood stars once stayed at this 1920s hotel, alongside ghosts that are said to haunt its corridors.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Wall after wall of this French seaside neighborhood is intricately decorated with seashells and corals.

The massive white mound and accompanying water terraces are a striking geological oddity.

A small marionette collection located within the dark cellars of an 11th-century Austrian castle.

A series of tiny artificial islands rich with produce bob atop the surface of the lake.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

The remains of a 1st-century aristocratic Roman town house featuring beautiful well-preserved mosaics.

One of its engravings is believed to be among the first representations of medical and surgical instruments.

This bustling Italian plaza is built on the ruins of an ancient Roman amphitheater.

A contemporary fresco movement illustrates the region's rich history.

This charming colonial alleyway is one of the oldest continuously used residential streets in the U.S.

Where Venice's gondolas go for a tune-up.

Mrs. Mallard and her brood are a beloved fixture in Boston Public Garden.