Soaring across some of the widest rivers and deepest valleys on the planet, bridges have always been at the cutting edge of engineering. We travel high into the mountains of the Colorado desert to find out why a hidden engineering masterpiece could disappear at any time. We ask why a stretch of overgrown concrete in a Czech reservoir is known as 'Hitler's bridge'. We find out how the highest bridge in the world collapsed in less than one minute. Finally, we uncover the story behind Cape Town's invisible bridge, which never carried a single vehicle.

• Saul David
• Tom Ward
• Fran Scott