We’ve gotten a lot of questions about bridges and tunnels: How do bridges stay up? How are tunnels built? How do they build bridges over water? How do they put tunnels underwater?

To answer these questions we’re staging a little friendly competition: bridges vs. tunnels!

We’ll find out how they’re built, where they’re found in nature, and what they may look like in the future. Plus: A visit from our friendly neighborhood robot.

SPOILER ALERT: Click here to learn more about this episode’s mystery sound.

Music in this episode by Podington Bear via Creative Commons.

Plus: Check out a tunnel boring machine in action!