What was once the largest NFL stadium.

This public baseball field is a beloved remainder from of one of the most historic stadiums in the country.

Controversial tribute to the heavyweight champion boxer who grew up in Detroit.

Over a thousand feet beneath the Detroit streets is a subterranean metropolis few are allowed to enter.

The fifth-longest suspension bridge the world, connecting one Michigan peninsula to another.

World's largest Christmas store.

These enduring murals depicting a distinctly Marxist tribute to capitalism could not even be defeated by McCarthyism.

Strange physical sensations and optical contradictions keep visitors coming back for more.

Island where motor vehicles are banned -- home to the only carless highway in the United States.

The Beaux-Arts aquarium boasts a vast collection of saltwater and freshwater fish on an island in the Detroit River.

This freshwater spring fills with 10,000 gallons of water per minute.

This impressive working clock made of 16,000 plants changes its flowers twice a year.

One of the largest underground systems runs under Canada's largest urban center.

One of the Seven Wonders of the Modern World holds the world's tallest metal staircase.

A 98-room castle in the middle of Toronto that bankrupted a 19th century electricity multimillionaire.

Breathtaking and huge 430 year old maps of Italy.

Famously misunderstood wonder of the ancient world

This Norman castle was once the site of a Victorian-era prison, and now exists as a luxury hotel.

Its collection includes a broad array of social, geographic, graphic design, and political history.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.

Scattered throughout London are ancient remnants of the city's former bounding wall.

Hear the quietest sound from across the dome.