An alleyway plaque is all that remains of the independent Texas' envoy that forgot to pay their rent for over a century.

A fantastic castle rumored to be the birthplace of King Arthur.

A historic house left in "dramatic still life."

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

This castle was established by the 4th Duke of Montrose and is connected to the Buchanan Clan.

Catacombs turned marketplace.

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

Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

Several plaster noses are hidden in plain sight around London's Soho neighborhood.

A special shop catering to the needs of things that go bump in the night, and also helps kids become writers.

The quaint little store that is said to have inspired a famous Dickens novel was only given its name after the book was released.

The longest hedge maze in the world.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

Rebuilt remains of a temple to Roman god Mithras.

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

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

Northern Ireland's Brobdingnagian stepping stones.

360° views of the city plus five floors of optical illusions and hands-on science.

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

The world's largest collection of witchcraft regalia.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

The sign at the garden gate reads: "These Plants Can Kill."

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

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