This is 99% invisible. I'm Roman Mars.

Every city in the world has something that makes it special,

but the ones that really capture my imagination are the cities with distinctive forms of transportation.

Venice has its canals, London its bright red double-decker buscars,

and the twin cities of Minneapolis and St. Paul have skyways.

In both cities, downtowns, there are vast networks of climate-controlled pedestrian bridges

that reach over the streets and connect a building to building on the second floor.

Here's how Minnesota Senator Amy Klobuchar describes them.

The skyways, of course, are the glass enclosed above ground tunnels that connect our buildings.

Because if you go outside in the winter, you will die.

That's right. And they're like a human habit trail.

Habit trail is the brand name of literal hamster tubes, and that's a pretty good description.

That's reporter and Minneapolis lifer, Katie Thornton.

Walk along almost any downtown street in the twin cities, and you'll see a series of these

enclosed glass bridges tying together huge office buildings and shopping centers.

Thanks to the skyways, you can park in a heated garage, go into work, run some errands,

maybe go to the gym, all in short sleeves, on a minus 20 degree day. People legitimately

brag about how many weeks they can go without stepping foot outside.

Downtown Minneapolis has the oldest and largest contiguous skyway network in the world.

There are nearly 10 miles of totally enclosed climate-controlled pedestrian bridges,

and Downtown St. Paul has its own massive system.

The skyways are integral to the twin cities sense of self.

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