A hidden subterranean installation offers a view of the sky.

Concrete strongholds stand guard over the Golden Gate.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

Macabre astrological automaton clock dating to the late 1400s.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

This tipsy office building in downtown Prague was originally called “Fred and Ginger.”

This artificial cave looks like something out of a fairytale.

Straight out of a nightmare, barcode-faced babies climb up and down Prague's television tower.

This riverside restaurant has been serving customers since 1146.

From Ancient Rome to WWII, Neupfarrplatz has over 2,000 years of history underneath its main square.

The ruins of a monastery where Saint Bridget of Sweden had her revelations recorded.

An American ghost town hides along a side street in Scotland's capital.

One of Edinburgh's oldest pubs hides a 19th-century skittles alley in the back.

Protecting the dead from opportunistic body snatchers.

The most loyal of little dogs, or a Victorian era publicity stunt?

Anonymously sculpted and donated, these sculptures made from poetry books and pages are sprinkled around the city.

The taxidermy remains of the first mammal ever cloned from an adult cell are on display in Edinburgh.

This obscure walkway links Edinburgh’s Old Town with one of the city's prime vantage points.

Some of the tallest ancient American ruins continue to inspire awe and curiosity.

The small peaceful island off the Venice tourist circuit is where the city began more than 1,500 years ago.

This community on a small Venetian island has taken to painting their houses in bright neon hues.

This Venice bookstore has resigned itself to constant flooding by keeping its books in bathtubs and boats.

This palatial spiral staircase was so unusual the name "snail" was given to the noble family who built it.

The marble facade hides a little-known medical museum with early surgical instruments and rare copies of canonical texts.