This sinkhole in the Arizona desert is filled with carbonated, arsenic-rich water

This hidden alley near the location of Rome's first theater was the site of a curious miracle.

This immaculately preserved church from late antiquity was originally the mausoleum of the Emperor Constantine's daughter.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

The only bridge in the United States where BASE jumping is legal without a permit year-round.

This historic bridge connects Whidbey Island to Fidalgo Island across whirlpool-filled waters.

The local club's soccer field is practically surrounded by UNESCO-protected monuments.

This pedestrian bridge in Croatia is a sleek, ship-inspired design with a fun net and social spaces.

The Metropolitan Police refurbished the blue box (perhaps not coincidentally) the same year "Doctor Who" returned to TV screens.

This South London cemetery holds the remains of more than 15,000 people.

After decades of damage, this feat of timekeeping and automaton art has been given a new lease on life.

The world's first funicular powered by a steam engine.

This post-Ottoman era church in Athens was built by locals to serve the residents of Anafiotica

This stone tower was built to protect Crete from incoming pirates.

Scores of wax baby figurines add an unusual mood to this beautiful church on the Greek coast.

The ruins of an ancient fortification wall sit in front of and underneath this boutique hotel.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.

Luminaries of all stripes have sipped strong Greek coffee at this cafe since 1839.

This 15th-century island fortress later served as home to the executioners no one wanted to live near.

The ruined doorway is a portal to the building's turbulent and torturous past.

This legendary city has been a tourist attraction for centuries.

Resting place and mausoleum of the founder and first president of Turkey.

A giant replica of an Assyrian cuneiform tablet stands in the middle of a busy intersection near the city center of Kayseri.