The most elaborate of 12 medieval arched doorways to the old city of Burgos.

This remarkable museum sprung from one of the most important prehistoric archaeological sites in the world.

A historic Christian shrine nestled within a spectacular natural cave.

A road that winds through this natural cave is the only way to access the small, appropriately-named village of Cuevas.

A magnificent place to see authentic paleolithic cave paintings that are an astounding 33,000 years old.

Stormy conditions send jets of seawater bursting through holes in the cliffs.

These primitive rock paintings include a very beloved depiction of a woolly mammoth.

The walls of these four caverns are filled with art that dates back to the earliest human presence in Europe.

This beautiful spit of land was once the summer playground of the king of Spain.

A small church ornamented with medieval erotic sculptures.

The facade of this 16th-century building is decorated with carvings of 300 seashells.

The Cathedral of Salamanca has a number of unusual carvings but none so surprising as a modern astronaut.

The ruins of a 2,000-year-old Roman fishing village perched on one of the best beaches in Spain.

Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

Bacteria and algae give the salty water its bubblegum hue.

Geological storytelling.

A Memphis park where you can walk the whole Mississippi River in one go.

This Memphis recording studio launched the careers of Jerry Lee Lewis, Johnny Cash, and Elvis Presley.

The winter home of millions of migrating monarch butterflies.

Dating back to the second century, vestiges of prehispanic mural paintings are found in this underground palace.

This Costa Rican topiary park is a surreal garden of unearthly delights.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.