This curious, round temple is the oldest still-standing marble building in Rome.

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

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

Originally built in the 15th century, this well gave the surrounding area its name.

On the Spree bank, discover one of the last reminders of a symbolic wall that divided, and was torn down by the people.

A fantastic castle rumored to be the birthplace of King Arthur.

This sculpture marks the spot where one of the greatest Roman rulers was proclaimed emperor.

These planks were originally installed to hold the dead.

This giant steel bear is a tribute to naturalist John Muir.

A double cantilever system bridge that was designed to prevent flood damage.

One of the most spectacular 18th-century bridges in Scotland.

This man-made waterfall was designed to help improve access for spawning salmon.

A collection of short standing stones covers this hillside.

This is the largest cemetery in Ireland and the first cemetery museum in the world.

This rare surviving broch is one of Scotland's most impressive Bronze Age structures.

This ruined travelers shelter sits abandoned in a desolate bog of Flow Country.

These ruins of a medieval church are full of architectural mysteries.

This macabre monument atop an ancient well gives a nod to a brutal episode in Scottish clan history.

This unusual rock looks like a giant, otherworldly mushroom sprouting atop a cave.

A small Scottish town's larger-than-life tribute to the celebrated accordion player.

One of two Irish-style round towers in Scotland, this structure has mysterious origins.

Macbeth's infamous "Great Birnam Wood."

This Birnam-based garden honors the legacy of 19th-century children’s book author Beatrix Potter.