Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

Sound travels strangely in this underground whispering gallery.

A Stockholm metro station is home to an escalator that is not only the longest in Sweden, but among the longest in the world.

Small Easter eggs are hidden in the ventilation holes of the city's newest trains.

This unique sculpture is often overlooked by pedestrians.

A temporary art piece to celebrate LGBTQ Pride is now a permanent part of Stockholm's traffic landscape.

Despite dreams of constructing this fairytale mansion, Albert Gotthard Nestor Cedergren never saw its completion.

The fastest way to send a message before electricity was invented.

This giant crucifix is like U2's Joshua Tree for Swedish death metal fans.

Three floors of musical instruments coming from all corners of the world and hundreds of years of musical history.

The concrete skeletons of an abandoned Swedish town hide among the trees.

Sweden's oldest animated sign is still lighting up the skyline today.

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

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

Head underground and take a tour of the city's working sewer system, and see the underground river Senne, which defined Brussels for centuries before being covered in the 19th century.

Lavish royal estate punctuated with heated greenhouses.

Legend says this fabled well held part of a mythical Norse tree.

Ancient burial grounds of the wealthy.

A subterranean house of worship carved right out of the bedrock.

Villas that once served as playgrounds for the rich now fall away in decay.

An alien church provides much needed silence in the midst of a Finland shopping center.

A lovingly curated curio shop in which the taxidermy wear newspaper party hats, and peanut shells are spread across every surface.

Housing a morgue, rare and confiscated weapons, and autopsy remains, the Vancouver police museum displays the dark side of Canada.

Community bookshelf of 25-foot-tall book spines.