The oldest housing complex in Riga is a mini timeline of architectural trends.

A black cat protests the City Guild in Riga's Old Town.

3,000 market stands in five former Zeppelin hangars.

Site of a classic 19th-century physics experiment to prove the earth is rotating.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

A Gothic-inspired fish market is Gothenburg's best place to find loaves and fishes.

The world's biggest floating museum in Gothenburg, Sweden.

This centuries-old rooster survived a devastating fire.

A concrete Picasso in the middle of a student housing complex on the outskirts of Stockholm.

Outside a Viking museum sits a modern-day runestone made by a Swedish runemaster using traditional methods.

The Swedish flag over this small naval fort signals that the nation is at peace.

Stockholm's narrowest alley is barely over two feet wide.

Sweden's "good old days" painstakingly re-created in a model village.

The library's graceful rotunda is like a bibliophile's temple.

It houses the remains of a 17th-century version of the Titanic.

Elaborate tile work in this railway station tells the story of Portugal.

A hidden three-foot-wide house separates these two regal churches.

The stunning interior of this Gothic church is covered in ornate gold details.

The doodles of a genius line the walls of a secret room under the Medici Chapel, where they were hidden for nearly 500 years.

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

A copy of the famous statue can be found in this Florence piazza, along with one of the most breathtaking views of the city below.

Two very green residential towers cleaning the air in one of Europe's most polluted cities.

A Nesting Doll of Churches.