The pretty iron lamp is a reminder of the architecture underneath London's streets.

Built over an abandoned train yard, this hidden gem is full of winding paths and offers gorgeous views of Sydney Harbour.

The commemorative stone column conceals a secret laboratory.

A computer bug so primitive it was an actual insect.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

A secluded art gallery hidden within the cellars beneath Tallinn’s medieval monastery.

This medieval Estonian tower provides access to a series of tunnels that have been home to soldiers, punks, and fine art.

A program of Communist glamour in post-Stalin Poland is preserved in this colorful museum.

A tribute to the Polish insurgents who fought in the failed attempt to end their city's Nazi occupation.

A rare tour of an aristocrat's private home reveals valuable 17th-century paintings from artists like Rembrandt.

Legend says a giant, venomous spider once dwelled within this Polish church.

A stunning silver lining to global warming's gloomy cloud.

The man who gave his name to magnetic measurement is buried in the city where he did his best work.

These beautiful objects represent beautiful ideas.

An illuminated manuscript comprising the life's work of a lone monk, inexplicably decorated with a portrait of Satan himself.

This open air cathedral invites all faiths to worship under the only roof big enough to fit them all: the sky.

A hidden bathhouse in one of Stockholm's oldest and busiest neighborhoods is open to anyone who can find it.

This tiny museum's sizable collection is jammed into a former underground public toilet.

Real bones which are said to have belonged to a Polish dragon.

This 17th-century pub once had a hole in its wall so the neighboring blacksmith could easily access beer.

This old medieval prison tower has been a site of astronomical research for more than 250 years.

The mysterious, fantastical woodland inspiration for "The Lord of the Rings."

These rare statues are one of the few remaining material witnesses to Old Prussian culture.

This antique thermometer honors the creator of the first universal temperature scale.