Inside this chapel, Victorian jailers took the separate system to new levels.

Modern commuters still pass through this 2,000-year-old Roman archway.

One of Oxford's greatest treasures likely belonged to the legendary King Alfred the Great.

This Norman castle was once the site of a Victorian-era prison, and now exists as a luxury hotel.

A theatre built to house the rowdy Oxford graduation ceremonies became the stage for a debate about God's existence.

This 11th century tower is said to be the oldest building in Oxford.

Used as an example in one of the first dictionary entries for "museum" in 1706.

J.R.R Tolkien, C.S. Lewis, and other "Inklings" met at the Oxford pub to discuss the now legendary fantasy stories they were writing.

Inside this art museum resides one of Glasgow's most famous musical instruments.

An icon of the Battle of Britain is frozen in flight in a grand Victorian museum.

A six-ton wedding present for the King of the Scots.

The final resting place of soldiers' loyal canine companions.

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

This equestrian statue of Constantine the Great has been the subject of criticism for centuries.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

Breathtaking and huge 430 year old maps of Italy.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

One of Mexico's least-visited archaeological sites is tucked away inside a theme park.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Every equinox this Maya pyramid puts on a spooky ancient light show.

Edison's cast-in-place concrete houses were a failure, but way ahead of their time.

Nassau Hall has served as army barracks, a museum, and played a key role in the American Revolution.

This Delaware River bridge is emblazoned with a catty slogan from a more prosperous time.

A playground inspired by differential calculus dangles from the ceiling of the Liberty Science Center.