Northern Ireland's Brobdingnagian stepping stones.

The largest of London's subterranean rivers and once a mad, bad center of London life.

A sanctuary for wolves in a community which once trembled in fear of the murderous "Beast of Gévaudan."

Gliwice Radio Tower, likely the tallest wooden structure in the world.

This beautifully designed star-shaped fort was the premier defense system of the late 1500s.

A roadside shrine to a late rock god only remains thanks to the unyielding efforts of his fans.

Lyon, France is home to two remarkably preserved Roman theaters, one dating back to 15 BCE.

Amazing and mysterious Neolithic settlement on Scotland's Orkney Islands.

The odd cement nubs littering this Spanish square are actually the entrances to a series of buried silos.

This remote eatery and museum is preserved as a time capsule of a small Icelandic fishing town.

These ominous lava formations were said to be an entrance to the netherworld so of course they inspired a famous metal band.

The summer tourists on these cliffs are thousands of seabirds.

The curious underground history of keeping Paris clean.

The Argonaute submarine was the French navy's pride and joy in the 1950's.

These mammoth-yet-narrow crevasses in the Earth are perfect for taking an otherworldly swim.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

One of Chile's most active volcanoes is riddled with beautiful caves.

This Vietnamese hell cave lets visitors take a walk through a devilish underworld full of demons.

World's largest cave was only discovered in 1991, and now offers tours to the public.

The world's longest outdoor covered escalator system transports commuters through Hong Kong's hilly terrain.

A cemetery and the town it served sinks beneath the sea during the volcanic birth of Mt. Vulcan.

This concrete ship has had four careers - World War I tanker, floating amusement park, fishing pier, and artificial reef.

An abandoned beach resort in Normandy reclaimed by artists.

A burnt-out motel with priceless Native American artwork in the basement, redeveloped into apartments.