I. B. Perrine Bridge

The bridge from the southwest side. slgwv (Atlas Obscura User)

Completed in July 1976, this steel arch bridge over the spectacular Snake River Canyon just north of Twin Falls, Idaho carries US Highway 93. The main deck is 486 feet above the river, making it eighth in height among United States bridges, and the main span is some 993 feet long.

It is named for Ira Burton Perrine, an early promoter and founder of Twin Falls. The current bridge replaced a cantilever steel bridge that had been opened in 1927. Pedestrian walkways on either side are separated by barriers from vehicular traffic and provide stunning views of the Snake River and its canyon.

The views alone make the Perrine Bridge worth a visit, but beyond that, it has an exceptional claim to fame: it is the only bridge in the U.S. from which BASE jumping is always legal without a permit. BASE jumping is an extreme sport in which people parachute from fixed objects, BASE standing for Buildings, Antennas, Spans (i.e., bridges), and Earth (i.e., cliffs, pinnacles, etc.). It’s considerably more dangerous than regular skydiving and is flatly forbidden in many if not most jurisdictions.