Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

For part of the year, this innovative greenhouse is painted white to keep the plants from getting scorched.

These murals stand as reminders to the troubled history of this Northern Ireland city.

These barriers stand as stark reminders of Northern Ireland's troubled past.

The only monument to name all of the passengers and crew who died on the RMS Titanic.

Northern Ireland's Brobdingnagian stepping stones.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

An often overlooked ancient site in downtown Athens with substantial history (and nature).

Legend says this sacred tree was a gift from goddess Athena.

This 15th-century island fortress later served as home to the executioners no one wanted to live near.

The hallucinogenic center of the ancient world.

A little sculpture with a large wardrobe.

This narrow Ghent alleyway is an officially sanctioned street art tunnel.

Highly spherical boulders on the shores of New Zealand.

Major tourist destination known for its bubbling mud-pools and hot thermal springs.

Only 68 people per day are allowed to visit this New Zealand bird-watcher’s paradise.

New Zealand's only running funicular railway.

The same water that fills a luxury resort’s pools feeds these free hot springs in the rainforest.

Also known as Uncle Karl, the beloved bronze copper keeps a watchful eye on St. Stephen’s Basilica while people rub his lucky belly.

Some of the greatest minds in the history of Hungarian art and science converged in this café.

Museum dedicated to the terror regimes of Hungary.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

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

Science meets wall art to highlight the beauty of famous mathematical equations.