In Florence's great Duomo, a 26 foot fresco honors a mercenary famous for attacking Florence.

The walls of this tiny Italian church are entirely covered with frescoes.

An open-air museum of 18th-century homes and churches transported from various villages in Southern Poland.

On this Polish road, an optical illusion makes cars seem to roll uphill.

The two abandoned overpasses are among the largest bridges in Poland.

This oddly beautiful water cistern is a techno-temple to the wet stuff and a multimedia masterpiece.

Come to this Polish museum to take a good, clean look at filth.

This fairytale medieval church in Poland originally spent centuries in Norway.

The largest toy museum in Poland showcases Europe's history of childhood.

This mysterious and once-grand memorial still embodies a remarkable architectural vision.

Boats must transform into railroad cars to navigate this Polish canal.

Poland's oldest salt mine has nearly everything one needs to live underground forever.

This centuries-old wooden wonder was built in less than a year and is one of Europe's largest timber-framed churches.

This hidden collection of everyday objects illustrates life within communist Poland.

This 700-year-old structure is one of the most unique architectural and historic monuments in Gdańsk.

The site of the first battle of World War II.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

A fairytale Gothic castle steeped in Nazi treasure conspiracy theories.

An underground city of salt.

This uber-quaint Polish village is known for its habit of painting elaborate floral motifs on just about everything.

Warsaw's fantastically preserved gasworks...almost.

The world’s narrowest house makes for an awkward, four-foot-wide living space.

A 20th-century picture show in 3-D.