Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

A spherical "micro-nation" in the heart of Vienna.

Op-art architecture designed for happiness.

This massive subterranean fissure is known as the "underground Grand Canyon."

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

One of the largest caves in the world open to the public.

A star-shaped fortress town fort built in the geometric model of the Renaissance utopian city.

A sudden, striking cluster of hills south of Padua has been attracting visitors for centuries.

A complex, nine-layer maze on the grounds of a Venetian doge's playground.

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

The oldest botanical garden in the world that technically isn't the oldest.

One of the world's oldest working clocks is curiously missing the Zodiac sign of Libra.

Something's missing between the arcades of the Palazzo della Ragione in "the city of the three withouts."

The tomb of the mythological founder of Padua is not hidden in some obscure crypt, but stands right in the middle of the city square.

The world's oldest surviving anatomical theater, where "the dead are pleased to help the living."

Built to repay the sins of the father, this church is home to one of the most valuable works of Western art.

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

This Roman statue is missing a limb from when the Venetians stole it from Constantinople during the Crusades.

Go inside to really appreciate this 500-year-old technological masterpiece.

This museum houses an imposing skeleton army comprised of creatures great and small.

A haunting collection of the vanished and disappearing natural world.

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

Known as the "Dodo Manège," this carousel features a herd of animals that have disappeared—or may be gone soon.