When it opened in May 1937, San Francisco’s Golden Gate Bridge was the longest suspension bridge ever constructed. Today, it only ranks 9th, but the gorgeous span remains the most photographed bridge in the world.

The Golden Gate’s 75th anniversary is being celebrated this month with numerous special events, including the California Historical Society’s exhibition A Wild Flight of Imagination: The Story of the Golden gate Bridge. The show, which runs until October at the Society’s San Francisco museum, comes with a very neat app and ebook which is available on iTunes for free.