These unusual rooms on wheels are holdovers from the 1960s.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

This train station inspired the name of a 1970's rock band and provided the backdrop for their album cover.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

This pre-Revolutionary War grist mill ground corn and flour for soldiers in seven American wars.

Stockholm's deepest subway station is also a stunning ecological wonder.

An ancient Viking runestone hidden in plain view in Stockholm's old town.

This small museum nestled inside a souvenir shop is dedicated to Sweden's most well-known toy.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

A 130-year-old urinal is the oldest of Stockholm and perhaps all of Sweden.

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

What looks like a birch tree smushed between two pieces of glass often confounds commuters.

Climb to the top of its spiral spire for spectacular views of Copenhagen.

Danish tourist destination well known for open stalls where vendors sell marijuana on the street.

This bridge's unique architecture honors nautical heritage and encourages self-awareness.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

The last Victorian market in Belfast.

The modern birthplace of Irish freedom.

These murals stand as reminders to the troubled history of this Northern Ireland city.

Northern Ireland's Brobdingnagian stepping stones.

This tiny train shuttles passengers to one of Northern Ireland's most spectacular sights.

It was once nicknamed "the most bombed hotel in Europe."

Belfast's namesake river still winds below the city center, hidden from sight.

The only monument to name all of the passengers and crew who died on the RMS Titanic.