Investigate a Michigan air base where a UFO cover-up allegedly took place, then wander through a wonderland built by a shady entrepreneur. Explore a California civil rights mecca and a Croatian cliffside citadel that influenced the fate of a nation.

Unearth a wartime nerve centre in Dover that made the UK proud, then visit a mansion caught in the crosshairs of the Civil War. Dig up an Estonian ruin's connection to Catherine the Great and explore the arena where Joe Louis boxed his way to fame.

Inspect a Scottish site that became a military flashpoint; an Oklahoma ruin where Native American cultural genocide took place; look inside a crumbling Greek house of horrors and an Oregon military facility that once battled an imaginary enemy.

View a decaying compound in the French capital that was the backdrop to an Allied great escape, then explore a Bulgarian propaganda factory. Theorize about an infamous murder scene in Malaysia and celebrate a Philadelphia artistic landmark.