The medieval castle built as headquarters for the Pope's secretive Knights Templar.

Burping, gurgling geothermal mud pots by the Salton Sea.

The splendor of this 17th century golden chapel has led it to be called the "eighth wonder of the world."

Haven for steampunks.

The highest point on the island known for buildings that touch the sky.

Erected in 1697 this Philadelphia bridge is the oldest surviving roadway bridge and perhaps the oldest stone bridge in the United States.

This elaborate towering structure was once famed for its revolutionary height.

The highest point in Delaware is located under a trailer so this marker across the street will have to do.

An Aztec temple, the largest man-made pyramid in the world, sits buried in earth with a Spanish church set on top.

The only home that Alexander Hamilton ever owned has a history almost as troubled as his own.

Twenty-seven massive radio antennas on the high plains of New Mexico search for life on other planets.

A one-of-a-kind sundial at the Very Large Array honors a radio astronomy pioneer, incorporating the original piers from his breakthrough radio telescope.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

Even Henry David Thoreau found this glacial pothole irresistible.

This lower Manhattan bar is set up in an old bank vault that rests beneath a skyscraper that hides even more historic splendor.

This high-perched pachyderm marks the memory of not one, but two elephants gunned down in small New England towns.

This replica medieval European village in the Dominican Republic was built by a Hollywood set designer.

This trio of Dominican cave lakes comprise a colorful biosphere of natural life.

The final resting place of Christopher Columbus - or possibly someone else.

Built in 1512, the oldest cathedral in the Americas.

The first official clock in North America, it kept time for the Spanish government of Santo Domingo.

These unassuming lighthouses have seen the first reading of the Pledge of Allegiance, the first wireless transmission, and more than one mystery.

One car at a time please.

A bit of retro transportation flair preserved in the world's largest department store.