The only arched bridge made of stone on the entire Mississippi River.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

Quite simply the largest tree in the world (by volume).

Monasteries on rock pillars, once accessible only by frayed ropes.

The hallucinogenic center of the ancient world.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

This bronze boar's snout has been rubbed to a golden sheen by visitors seeking good fortune.

This massive mall has hundreds of shops, an amusement park, and a history of deadly amusement attractions.

As if T-rex wasn't big enough, this Canadian monument is four times larger than the real thing.

A memorial to the most decisive Native American victory of the Plains Indian War.

This record-setting hydraulic dam in the Montana badlands was one of FDR's most ambitious public works.

This small museum is home to some of the oldest and best-preserved dinosaur specimens found in Montana.

A smoke stack so large, the Washington Monument could fit inside!

A small Montana town commemorates the dog who waited at the train station every day for his owner to return.

Spectacular views await visitors to this lake.

These giant metal horses graze on a hilltop near the Montana highway.

New fungal and bacterial species call this deadly lake home.

This large garden vase urn has nothing to do with the seventh U.S. President—it was designed by one landscape designer to honor another landscape designer's contributions to the National Mall.

The house where Lincoln drafted the Emancipation Proclamation.

Engraved in stone here are the signatures of everyone who signed the Declaration of Independence.

Ruins from the Parthenon and petrified wood line the interior of one of the world's most famous monuments.

The hippo that stands on this university campus was once a drunken flea market purchase.

On the Fourth of July this area will transform into a Pompeii-like storm of falling embers and ash.

A gift from Japan, 17th-century lantern stands among the cherry trees at D.C.'s Tidal Basin.