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Photo: David Liu, CC BY-SA 3.0 via Wikimedia Commons
Beautiful, private garden. Very similar to the Los Angeles County Arboretum, but smaller and more intimate. Make sure to visit the International Rosarium with over 3,000 roses.
Descanso Gardens is a 150-acre (61 ha) botanical garden located in La Cañada Flintridge, Los Angeles County, California. It sits on the northern edge of the San Rafael Hills.
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This is a national laboratory run by Caltech complete with a security check point. JPL is the leading U.S. center of robotic space exploration. JPL focuses on the exploration of Mars with its Mars rovers. JPL does have an annual Open House that is held on or around Memorial Day weekend (last weekend in May). During this event it is open to the public, anyone can go at that time. Other times it is mostly closed to the public at large though some tour options are available through JPL Public Services Office for groups and individuals on an advance reservation basis.