A view-altering observatory at the University of Texas.

This hidden stream beneath Indianapolis makes an appearance in the best-selling novel "Underground Airlines."

Roadside Americana, fairy tale characters, and Austin quirkiness come together at this magical course in the heart of Texas' capital city.

A small and surprising passageway in Saint Petersburg devoted to the Beatles.

An abandoned masterpiece of Soviet Brutalist architecture.

Some Moscow residents once claimed the bizarre, contorted mass of metal on top of the building was used to manipulate minds.

Back in the tiny USSR.

This huge metal monument is slowly being stripped to its concrete skeleton.

The avant-garde design was able to bypass strict Soviet regulations on architecture.

Unusual building appears to be haphazardly built from randomly piled bricks.

Terrifying derelict military hospital once housed a recuperating Hitler.

One man has carved a number of natural New Mexico caves into psychedelic sandstone temples.

Hidden in an Italian forest is a completely homemade amusement park that has taken a lifetime to create.

An unfinished tomb carved into a giant boulder in the Arabian Desert.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

A long spiraling walkway winds through the woods, and around a copper beech tree at the center.

This painted Lego bridge is the product of over a century of locomotive history.

Ruins of a German Castle on top of a towering stone pillar.

The largest brick bridge in the world.

A portable, wooden replica (minus the hyphen) of Hamburg’s iconic crooked coffee shop.

A traditional U-Bahn station in Berlin gets a string of rather untraditional benches.

The music is over at the Ballhaus Riviera Ballroom, but the ballroom remains in haunting disrepair.

An abandoned meat mecca now serves as an excellent locale for urban exploration.

A crumbling Beaux Arts monument to the Bay Area's age of rail.