This macabre monument atop an ancient well gives a nod to a brutal episode in Scottish clan history.

One of the oldest reform schools in the United States, home to wayward boys such as Merle Haggard, now abandoned.

A popular tourist cave with a dark past.

Where the writer penned his famous story about a jumping frog.

Colorful lights and mirror-like brine pools create trippy illusions within the historic mine.

The world’s largest underground marble quarry is hiding in Vermont.

A cozy bookstore is tucked within an old gold mine shaft beneath the cafe and ice cream shop.

This ancient monastery complex was transformed from an island to a peninsula when the lake was partially drained.

A Christian retreat founded to welcome refugees fleeing from the Nazis during World War II.

A sprawling ancient Jewish cemetery with over 30 rock-hewn burial caves.

A spiritual sanctuary in a natural cave.

This peculiar border irregularity is the only way to legally enter Russia without a visa.

A wooden statue of an Estonian pagan god and King of the Setos stands atop a sacred hill.

Man-made mineral caves house massive bat colony.

A trio of giant wooden megaphones turn up nature's volume in this Estonian forest.

Hundreds of small crosses have been carved into the bark of the trees outside this small Estonian village.

This 15th-century cave complex is one of the very few monasteries to stay open throughout World War II and the Soviet regime.

A raised boardwalk winds through a thicket of stunted, century-old trees no more than nine feet tall.

Celebrating the transformation of trash into objects of beauty.

Experience Larry Spring's self-taught "common sense" laws of physics.

Brisbane's manmade urban beach has enough water to fill five Olympic-sized swimming pools.

One man's eclectic collection of treasures found at sea.

An early work of the architect Álvaro Siza Vieira, these swimming pools blend into the beach.

A historic cave in Scotland once served as a hiding place for a famous Covenanter.