Never actually a tree at all, this spot was the site of London's public hangings for nearly 600 years.

On this wooded path, a stained-glass window creates a spellbinding forest cathedral.

The sculpture is made of more than 100,000 knives collected to raise awareness about violence.

Human-made caves excavated to hide a secret society of wealthy pagans.

A little slice of Japan and its aesthetics in London's Holland Park.

Harry Potter once visited this massive limestone cliff, which was carved by an ancient glacial river.

The names Lúthien and Beren can be found inscribed on the shared grave of the famous writer and his beloved wife and muse.

A house of bones — but nobody is quite sure to whom they belong.

The largest cave chamber in Britain—big enough to fit a whole cathedral inside.

A metal tree emits eerie, melodic notes on top of Lancashire's Crown Point.

One of the world's largest collections of pathological specimens.

Surreal riveted sea forts once protected the Kent shores from German attack.

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

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

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

Its collection commemorates the author of the iconic children's book "Heidi."

In memory of The Blur Building, the temporary exhibition pavilion of vaporous nothingness.

A unique collection of Swiss art brut and naïve art displayed in an old warehouse.

A rare museum dedicated to a rather overlooked material in the history of fashion.

An amazing collection of rare wind instruments where visitors can give the iconic Swiss Alphorn a toot.

This little museum is packed with information about the region's past and present biodiversity.

A trove of ridiculously valuable prints and manuscripts under one roof.

A 13th-century Swiss castle houses a collection of artifacts from the Polish diaspora.

This colossal couch is an unlikely monument to Europe's first female Doctor of Law.