The USA's National Park Service celebrates its centenary this week. We've picked out eight of the best visitors centres and amenities designed as part of its Mission 66 project, which took place 50 years ago (+ slideshow).
Mission 66 was a 10-year building programme that aimed to expand visitors services to the parks in the decade before 1966 ? the 50th anniversary of the creation of the National Park Service.
Architects and studios including Richard Neutra and the Frank Lloyd Wright-endorsed Taliesin Associated Architects were chosen to design structures across the country. Most were built in the Mid-Century Modern style popular at the time.

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Another 50 years on, many of the structures are listed on the USA's National Register of Historic Places, and continue to provide information and facilities for their locations.
However, some have been controversially demolished, like Neutra's Cyclorama Building at the Gettysburg site and Henry M Jackson Visitor Center at Mount Rainier.
Regardless of their fate, here are eight of the most architecturally significant structures:

Cyclorama Building, Gettysburg National Military Park, by Richard Neutra, 1962
Photograph is by Wikicommons user acroterion
Richard Neutra ? responsible for some of California's most celebrated Modernist buildings ? was chosen to design the visitors centre on the site of the significant 1863 American...