The oldest volcanology research center in the world.

The only museum with its curator—and her pets—buried inside.

Ancient cave tombs known as the "houses of fairies."

142 ceramic steps become a mosaic once a year.

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

"Stairs of the Turks", a chalky white cliff eroded conveniently into stairs, allowing for easy pillaging.

These "anatomical machines" are only one of the many strange items in this Italian crypt.

Jesus' footprints and the first catacombs in the world.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

The underground sanctuary of a mysterious ancient cult.

Thousands of well-dressed mummies below a monastery.

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

Auguste Maïcon, a pioneer in French aviation, was born in this house in 1891.

The celebrated eyesore created by starry-eyed sweethearts.

Lyon's miniature version of the Eiffel Tower was built as a statement in support of French secularism.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

This unusual piece of Renaissance art depicting the bodily horror of crucifixion and skin disease may have been inspired by fungus-induced hallucinations.

This remarkable checkered church on a Corsican hilltop is fabled to have been built by angels.

France's highest manned weather station is the only one still inhabited by meteorologists.

Sky ships, planes, and portraits left as unique tokens of hope and thankfulness.

The eclectic observatory castle of a 19th-century astronomer and explorer.

The largest crypt ever constructed in France was built in the 11th century on an ancient Druid sacred site.

This church sits upon a peaceful hill and a long, turbulent history.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.