The world's toughest modern Christian pilgrimage leads directly to the gates of Hell.

A speakeasy takes on Chicago's drinking culture.

An ethereal glowing blue ocean cave in Croatia.

An Australian lake whose pink hue defies scientific explanation.

A wonder of natural limestone formations etched by millions of years of natural interaction between rainfall and rock and air.

The largest underground church in Europe.

A marvel of Byzantine engineering under the streets of Istanbul.

Limestone caves with spectacular showcase chambers.

A Collegiate Gothic quadrangle that surrounds an 18th century secondary school whose financing came from the likes of Alexander Hamilton and Aaron Burr, among others.

Skeletons dressed in extravagant 18th century royal costumes cavort in the aisles of this German basilica.

This strange geological landscape erupts with sudden bursts of water.

Preserved Inca city and site of the last Inca stronghold against the Spanish conquistadors.

Interactive modern and vintage submarine equipment, World War II relics, and submarine attire.

Two churches shoot bottle rockets at each others' bell towers in an unusual Easter celebration.

This dilapidated castle-like structure overlooks the Hudson River at one of its widest points and was once home to nuns.