This Philly landmark has a giant butterfly pavilion, three floors of insect displays, and withstood a $40,000 heist.

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

Mural made of 100,000 pieces of hand blown glass, and until recently, the largest glass mural in the US.

Once thought to be the mysterious work of a witchy prophetess, a well with unusual properties turns objects into "stone".

This magnificently macabre shield shows the power of chivalrous love in medieval times.

This intriguing Bronze Age artifact spent centuries hidden within a Welsh faerie hill.

This mysterious and unique painting is filled with symbolism.

Graffiti from the 16th and 17th centuries cover the walls of this part of the Tower of London.

Hidden in the courtyard of the Victoria and Albert Museum is a little-known tribute to two celebrity pooches.

The gigantic skull of a long-extinct species that once roamed the forests of England and Ireland.

One of the figures in this Celtic sculpture continues to puzzle archaeologists.

Buried for centuries, this hidden cellar is all that remains of London's medieval Whitefriars Monastery.

This Viking gravestone carved in a rare runic style was dug up from a London churchyard.

A labyrinth hides in plain sight at each of the city's 270 Tube stations.

The library houses an incredible collection of some of the world's most impressive books and manuscripts.

Historic church where a number of Shakespeare's actors are buried.

A unique tribute to the millions of animals who served and died for the British military.

William Blake claimed to have painted this gothic masterpiece after encountering this nightmarish being in a vision.

The 2,000-year-old beam is tucked within the pedestrian entrance to the old London Bridge.

Murals of the wild parties once held on the frozen River Thames.

A Roman spa buried deep beneath the City of London.

Three small rooms at the back of the “official” church of London's clowns.

Art Deco and “Wrenaissance” mash-up, this recently restored royal residence has been home to kings and comes with secret monkey passages included.

Ship-sized kinetic sculptural fantasy.