Some call this eerie forest of crooked trees the "Bermuda Triangle of Romania."

This sprawling bookstore spans four floors and has more than a million books in stock.

A network of concealed passageways lies within a busy London Underground station.

This landmark church concealed a crypt packed with bones that was discovered thanks to the London Blitz.

A clock designed to run with perfect accuracy for 10,000 years.

A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

A kaleidoscopic warehouse-maze of handmade neon signs.

This little museum is making sure that the art and history of the graffiti sticker is not scraped from history.

Berlin's old airport.

The skeletal frame of a decommissioned gas-pumping station offers breathtaking views of greater Berlin.

These former Nazi anti-aircraft towers offer a singular view of the north of Berlin in the summer, and a sanctuary for bats in winter.

A 12th-century fortress containing some of Berlin's oldest buildings.

A unique Holocaust memorial tells the personal stories of the Jewish residents exiled from greater Berlin.

Super-heavy Nazi architectural experiment.

A tree-like building perches on its trunk in the Steglitz neighborhood of Berlin.

A narrow passage next to a cafe leads to a courtyard exploding with murals, tags, and paste-ups.

A surreal museum of extraordinary industrial objects.

A slice of central Asia in the middle of Berlin.

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

These morbid carvings remind churchgoers of the inevitability of death.

Where condemned pirates met their grisly end at the gallows on the River Thames.

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

This marine reptile was discovered by one of the 19th century's greatest fossil hunters.