A guitar mounted on a wall in Temple Bar honors the Irish musician.

This ancient fort has been a great insight into the Roman presence in the region.

Experience what life was like in Ireland during the Viking and medieval ages.

Once used to calculate the various levels around the country.

A small alleyway with an unusual moniker.

The remains of a convent turned military barrack in the heart of Madrid.

This medieval castle is filled with an eccentric collection that ranges from ancient Egyptian artifacts to taxidermy to a mummified hand that was cut off during a duel.

This bronze statue was dedicated to a 1966 Beatles hit.

Be on the lookout for the symbolic insect all over the city.

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

Eighty million natural history specimens call this gargantuan museum home.

The popularity of Sherlock Holmes led to the creation of his fictional address, turning the orderly London street numbers askew.

Maybe the only restaurant in the world where your seat will be signed by a Nobel laureate.

Just like in Hollywood, Madrid has also a forgotten walk of fame.

This 47-story "M" needed 20 years to be completed

An 11th-century runestone decorates the halls of Terminal 2 of this Scandinavian travel hub.

Enormous ants wielding giant pine needles guard a Stockholm real estate company's office.

One of the world's oldest continuously operating meteorological stations sits on a hill in Stockholm.

When this 18th-century observatory's meridian was moved, it set Sweden's time back by 0.04 seconds.

Inside this church, a monument honors the first burial site of the famed philosopher.

Sweden's oldest animated sign is still lighting up the skyline today.

Sound travels strangely in this underground whispering gallery.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

Although rarely used, there is still a hidden room for the royal family at the Stockholm central station.