An 18th-century Spanish watchtower made entirely of seashell and concrete.

The third tallest lighthouse in America once guided author Stephen Crane to safety.

A building so large that it has its own weather.

A Circus legend leaves an unexpected endowment.

Former utopian colony based on the belief that the universe exists in a hollow sphere.

A mysterious castle built as a monument to lost love.

The famous boat that once ferried Bogart and Hepburn still floats in Key Largo after being abandoned for years.

Island ghost town detailing Flagler's folly in building the Overseas Railroad.

The largest freshwater lake in the Florida Keys.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

A monument celebrating the idea of reaching inaccessible places.

The island residents are known for taking their quirky sense of humor with them to the grave.

The former home of the Nobel Prize-winning American writer is now home to dozens of six-toed cats.

A small poultry graveyard in the courtyard of a popular Key West watering hole.

The ancient tomb acts as a calendar that keeps perfect time.

Dublin's "Dead Zoo" serves as a window to Victorian museum design.

The world's only flying boat museum honors a small Irish village that sent 20th-century aviation to new heights.

A hugely vast Irish landscape of barren rock that stretches for miles.

This single room has survived the centuries with almost no deterioration.

This singular Irish dolmen is more Frank Lloyd Wright than upright stonehenge.

An Iron Age fort on the edge of a seaside cliff offers a glimpse into an ancient, mystical world.