Comets

Test pilots and engineers embark on the first flight of the largest airplane ever built: the Stratolaunch, a one-of-a-kind aircraft designed to transport rockets, spacecraft and experimental hypersonic planes into the stratosphere.

Engineers in China are constructing the largest and most ambitious water transfer project in human history, defying nature to move vast quantities of water from the south to the dry north in Beijing, all without the use of pumping stations.

Explore three battlefield behemoths that command land, sea and air.

Inside access shows how an engineering marvel lifts boats to new heights.

Discover why the world's strangest disaster zones were built and abandoned.

New discoveries reveal what really happened in a remote Louisiana swamp.

New discoveries reveal what really happened on the shores of Lake Michigan.

New discoveries reveal why an island with a dark past was built.

Experts reveal the sinister purpose of a strange bunker in Florida.

A castle was the site of horrific murders perpetrated by a countess.

Experts reveal the role towers in Greece played during violent feuds.

Experts reveal why a massive, alien-like fortress was built.

An abandoned prison has evidence of a chaotic riot.

An eerie set of buildings in Paris is evidence of an unspeakable evil.

A notorious dictator's paranoid fantasies created a strange bunker.

An underground labyrinth can warp the mind and turn friend into foe.