The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

This colorful statue welcomes visitors to a Barcelona park.

An early 20th-century bullring converted into a modern shopping center.

A bookstore dedicated to the intersection of comedy and art.

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

Nicolas Schöffer's massive interactive sculpture was assembled in 1961 and brought back online in 2016.

This abandoned Belgian fortress is purposefully being left to nature.

A secret hatch containing two parchments was discovered in this statue over 40 years after its installation.

The tallest mountain in mainland Netherlands isn't actually very tall.

Stone memorial that's said to predict the death of the pope and the site of the Cadaver Synod.

A Nesting Doll of Churches.

This ancient market is often referred to as the oldest shopping mall in the world.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

A large replica of a monumental Roman inscription is located on the side of this museum.

This small church was constructed over the ruins of three temples dating to the Roman Republic.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

An 18th century fountain and two columns are all that remains of Rome's forgotten river harbor.

A monumental fountain in Rome features a large statue of Moses that has been criticized for centuries.

This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

Romans decided this 16th-century "talking statue" was so ugly, they named it after a primate.