This Florida sinkhole hides a rainforest-like micro-environment in its depths.

A mysterious castle built as a monument to lost love.

An underwater statue of Christ blesses the depths off Key Largo.

This 140-year-old beacon off the Florida Keys marks the wreck of a Navy ship that once roamed the Caribbean hunting pirates.

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

A monument celebrating the idea of reaching inaccessible places.

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

Archaeological sites and great food inside the island's largest mangrove forest.

The abandoned remains of this once-thriving hotel looms over the city, awaiting an uncertain future.

This colorful gate stands as an entrance to the walled city of Old San Juan.

Legend tells how a Spanish soldier disappeared from this isolated sentry box without a trace.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

The crumbling remnants of this 19th-century quarantine hospital hint at the touristy island's darker past.

This small fort played a huge role defending Puerto Rico’s capital city.

The bat-covered home of one of the world's most popular brands of rum is located on a tropical Art Deco campus.

Enjoy the waters of this half-moon-shaped natural pool surrounded by breathtaking scenery.

The short hike is worth the stunning views and crystal blue waters of a secluded beach.

Rusting, graffiti-covered tanks litter the beach of this island, once used by the U.S. military for target practice.

The world's brightest bioluminescent bay.

A magnificent waterfall nestled in the heart of the El Yunque National Forest.

A collection of massive stacked rocks in Texas includes a snarky note on the benefits of modern technology.

Legend has it the commander of the defenders drew a fateful line in the dirt with his sword just before the final battle.

Two small markers remember the Alamo's feline protectors.

The final resting place of American icon Buffalo Bill, and a museum that aids in telling his tale.