A massive rock in the surf steeped in legends.

An architect transformed this abandoned cement factory into his castle-like workshop.

Now a public art piece, this curious metal feature originally advertised a tinsmith's services.

This tree was grafted from the actual tree that led Isaac Newton to ponder the theory of gravity.

A treasure trove of astronomical, mathematical, and scientific instruments at Cambridge University.

One of several Lilliputian portals that are ready to transport passengers to other dimensions, if they can find them.

Edison's cast-in-place concrete houses were a failure, but way ahead of their time.

It took years to decode its mysterious messages.

A breathtaking 19th-century trail overlooks Lake Tahoe.

Perhaps the most spectacular grotto along the Algarve coastline.

Seven mini rowhouses fill the gap between 54 and 70 Westerstraat.

The only remaining historic maritime signal station in the United States.

The world's oldest known salt mine.

Poland's oldest salt mine has nearly everything one needs to live underground forever.

The world's second largest salt mine, said to have been discovered by Alexander the Great's horse.

Cathedral carved out of salt, located a mile below the earth's surface.

One of the world's largest salt caves is filled with fragile salt sculptures, salt rivers, and huge salt megadomes.

A salty cave excavated by elephants and the location of a deadly disease vector.

Gigantic Romanian salt mines used to heal respiratory conditions.

This beautifully deceptive waterfall is something far different from what it appears to be.

A museum dedicated to a sea that should have never been.

The oldest bar in Missouri is hidden within a limestone brewery cellar more than 50 feet underground.

A small "palace" and museum made of, and devoted entirely, to salt.

Over a thousand feet beneath the Detroit streets is a subterranean metropolis few are allowed to enter.