One of Antoni Gaudí's least-visited works, an homage to Catalan patrimony that mixes neo-Gothic with Modernista forms.

One of Europe's largest supercomputers is housed inside of a disused chapel.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

A mysterious artist-run cabinet of curiosities and library.

The remains of Crystal Palace Great Exhibition of 1851.

A cluttered and astounding collection of antiquities and curiosities.

This wildly-tiled artist's palace is a living and growing account of the creator's life, loves, and labors.

Remnants of a Victorian garden feature sitting in public woodland.

The anatomical-pathological collection of a man who changed surgery.

A makeshift shrine to the late rock star is still kept up on the nondescript façade outside 1 Logan Place.

An unusual round church in London with a Templar past.

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

A tongue-in-cheek arcade where the games are based on everyday life.

An 18th-century post box used to alert the church of sick and ailing foreign pilgrims.

Legend has it that this bronze orb, which sat atop an ancient Egyptian obelisk, once held the ashes of Julius Caesar.

A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

This ancient market is often referred to as the oldest shopping mall in the world.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

This sturdy, circular stronghold served as one of the forts that protected the Venetian Lagoon.

The pile of books behind the dignified writer gave the statue a most undignified nickname.

100 year tradition of fist fights, marked by marble footsteps.

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