Craggy concrete faces are hidden in the walls of this artificial cave along the San Antonio River.

Soldiers honored the beloved Pat with a special grave.

An ivy-covered arch bridge dedicated to Tejano music singer and legend Rosita Fernandez.

An abandoned, decaying sculpture garden built by an eccentric physician in the 1920s now looks more like a forgotten cemetery.

A gorgeous garden oasis with winding paths, stone bridges, and a troubling history.

A unique set of caves that spits waves back out into the ocean.

Images chiseled into the basalt here date back an estimated 300 years.

Once the site of the Hawaiian monarchy, this building was originally designed as a palace.

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

The spot where the namesake of the Douglas fir met his mysterious end on a Hawaiian volcano.

A model of a galactic embassy is hidden in plain sight along the highway, proposed by a UFO religion to find the aliens that created life on Earth.

A cooled lava flow from the Haleakalā volcano formed these surreal-looking columnar basalt structures.

A prehistoric landscape hidden in the cliffs of Maha'ulepu.

The sea urchin sculpture is an unusual commemoration of a New England town's seafaring history.

These abandoned waterworks are crumbling into the Potomac River.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

The preamble to the U.S. Constitution written entirely from vanity license plates hangs in the Smithsonian museum.

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

There’s a special club house at the top for the bell ringers.

The monument's pointy aluminum tip has been melted down by repeated lightning strikes.

Go take a picture with the inventor of the daguerreotype photographic process.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

The most decorated dog of World War I is preserved in the Smithsonian.