Submerged lava formations create incredible waterworks.

These picturesque Hawaiian falls are home to a rare species of fish that uses a special sucker to climb up cliffs.

Football field-sized microalgae production tanks on the Hawaiian coast create a stunning view from space.

This unusual lava tube spouts seawater during high surf.

A once-glowing grotto at the bottom of Waikapalae Wet Cave.

A mysterious inscription may hold a clue about the "Lost Colony" of Roanoke.

The mysterious 855-foot zigzagging stone wall has been baffling people for centuries.

Two flush headstones mark the only known graves to be embedded in an airport runway.

This stone is a marker of one millionaire's personal vendetta against gravity.

Incredible miniature towns and buildings created and decorated with thousands of tiny rocks.

The perfectly named cave drop is the deepest in the continental United States, almost matching the height of Seattle’s Space Needle.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

The "worst battleship ever built" is enjoying a grand second act, submerged 30 feet in the Gulf of Mexico.

An underwater statue of Christ blesses the depths off Key Largo.

Welcome to old Florida, where a 1940s mermaid show is still enchanting visitors.

The only swimming pool listed on the National Register of Historic Places is emptied and refilled each day with naturally filtered water.

The hidden offices underneath Memorial Bridge have been locked up since 1976.

In the basement of the U.S. Capitol Building is a hidden storage room full of ornate floor tiles leftover from the 1850s.

There just so happens to be a court even higher than the U.S Supreme Court: a basketball court in the building itself.

An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

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

Obscure Freemasons still live in D.C.’s largest private residence.

Daredevil repair workers can worm their way out the access hatch, loop ropes over the apex and rappel down the monument.

An Industrial Revolution-era public work that purified water using nothing but sand.