The site of a defunct mill, that once supplied marble for the construction of the Lincoln Memorial.

This high desert botanical garden is a unique display of Northern New Mexico's geology.

This hidden fire lookout offers spectacular views of Sequoia National Park.

A 19th-century cabin built into a hollowed-out Sequoia tree.

This double-arched masonry highway bridge is the only structure of its kind in Minnesota.

This slumbering beast honors the Bavarian soldiers who died in Greece during a 19th-century typhoid outbreak.

The 80-foot tire that looms over Michigan's I-94 was once a Ferris wheel in the New York World Fair.

One of the few working locomotive roundhouses in the United States.

An annual festival celebrating Colorado's most famous frozen corpse.

These decaying bridges 1,000 feet high are a reminder of the skill it took to cross the Colorado Rockies by rail.

This old train trestle and collapsed tunnel once allowed the railroad to negotiate the steep slopes of the Colorado Rockies.

The partially submerged ruins of a white marble quarry used in ancient Greece for over 1,200 years.

A unique arch graces the Dolores River Canyon near the Hanging Flume.

A remote sandstone plateau named for a legendary cattle rustler.

A river runs through this remote valley in a very unexpected way.

The decaying ruins of a failed mining company’s water diversion project cling to the side of a desert canyon.

An enthusiastically interactive mining museum that won't let black lung ruin the fun.

An ADA-accessible trail and deck offering stunning views of Colorado’s Mount of the Holy Cross.

The remnants of the base where US Army troops learned how to fight in extreme conditions.

A small collection of iguana-infested ruins hides amid Cancún's bustling hotel zone.

Few of the many visitors to this resort town know of its hidden Maya ruins.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

A Byzantine-era church hidden in a wooded area below the Acropolis.

The site of the "Bone Wars" between two rival paleontologists during the dinosaur rush of the 19th century.