Scattered throughout London are ancient remnants of the city's former bounding wall.

Eighty million natural history specimens call this gargantuan museum home.

Hear the quietest sound from across the dome.

One part local history, 99 parts gruesome haunted house.

An unusual round church in London with a Templar past.

A hands-off space for graffiti artists to hone and display their skills.

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

The modern birthplace of Irish freedom.

The comedy and tragedy of Oscar Wilde is preserved in a Dublin park, captured in a sculpture of colorful stone.

Amidst the bustling streets of Dublin, there is a hushed garden that is dedicated to "All those who gave their lives in the cause of Irish Freedom."

Dublin's "Dead Zoo" serves as a window to Victorian museum design.

This permanent collection of preserved bodies taken from Irish bogs is one of the leading authorities on such morbid mummies.

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

Amsterdam's former hotspot for public executions and dissections.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

A public urinal so pretty, it was declared a national monument.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

The former home of a mad diplomat is said to still be marked in bloody, arcane scrawls.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

The attic of a four-century-old canal house hides a clandestine church.

The history and future of cannabis.

A floating cat sanctuary on an Amsterdam canal.

Established in 1638 to battle the Black Death, Hortus Botanicus Amsterdam is a treasure trove of rare flora.

Museum preserving torture methods from the past.