A striking glass tribute to two sisters who suffered during Scotland's "Killing Time."

This tiny train shuttles passengers to one of Northern Ireland's most spectacular sights.

The last Victorian market in Belfast.

This alley off Edinburgh's Royal Mile contains remnants of the city's seedier history.

The ruins of this Dutch castle sit atop a labyrinth of once-secret tunnels and passageways, dating back over 900 years.

Visit the ancient, mysterious Roman catacombs ... in the Netherlands.

This Roman relic was discovered in Scotland by a mudlarking ferryman.

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

A beautiful Greco-Roman structure houses a well once believed to have healing powers.

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

One of the largest lenses of its kind ever created, this former ship beacon has been brought down to Earth.

This sculpture commemorates Edinburgh's sister city and their respective celebrity dogs.

A sweet symbol marks the place where torturous executions were once carried out.

The fountain marks the area where hundreds of accused witches were burned at the stake.

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

This 17th-century street hidden beneath Edinburgh was once a breeding ground for the black death.

This 16th-century house tells the city's history through old artifacts and quirky tales.

The taxidermy remains of the first mammal ever cloned from an adult cell are on display in Edinburgh.

The dance of this huge clock is a magnificent and eerie commentary on good and evil in the history of humankind.

Every birth, death, and marriage is recorded in these color-coded leather-bound books.

This massive monument has been telling the time for 150 years—at a slight angle.

The world's first experimental nutritionist is memorialized as the "Hippocrates of naval medicine."

Once home to a Scottish baronet, this 18th-century historic house doubles as a legendary art space.

One of the oldest scientific gardens in Britain, containing more than 13,302 plant species in its core collection.