The entire length of the border is marked by a 20-foot-wide slash through the trees.

Minnesota's oldest and deepest mine is now an underground physics laboratory.

Terraced flowerbeds and rock sculptures in the midst of the Minnesota wilderness.

Live long and prosper in Vulcan, Alberta.

Standing at 21-feet tall, this space cowboy adds to the legacy of Route 66's muffler men.

This 1930s-era Route 66 Tulsa landmark was moved, restored, and filled with neon.

A beautiful geyser under environmental threat.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

The fifth-longest natural arch in the world, and the longest outside China.

An atomic bomb-proof strongbox protects the U.S. Constitution from terrorists and thieves.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

These moss-covered medieval ruins tower atop the smallest of Ireland's Aran Islands.

The highest point in the state of New Hampshire, and while unlikely "the worst weather in the world," it sure seems that way to hikers.

This 19th-century building inadvertently preserved the handprints of its builders within its walls.

The highest point in Tennessee, Clingmans Dome bears witness to the ravages of one type of insect.

The only road through the heart of Glacier National Park.

The source of America's longest river is also a historical landmark and the start of a famous nude run.

At this Minnesota state park you can easily wade across the source of the mighty Mississippi.

These markers are used to document elevation changes around the famed dam.

Thomas Jefferson's estate is home to hundreds of varieties of historic fruits and vegetables.

The tomb was guarded by soldiers from both sides of the war, and some left their initials carved in the brick.

The graveyard holding the remains of George Washington's slaves was forgotten for nearly 200 years.

Look closely and you’ll notice that the color changes a third of the way up the tower.