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Phipps Conservatory and Botanical Gardens is a complex of buildings and grounds set in Schenley Park, Pittsburgh, Pennsylvania. The gardens were founded in 1893 by steel and real-estate magnate Henry Phipps as a gift to the City of Pittsburgh (source: Wikipedia).
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Phipps Conservatory and Botanical Gardens in Pittsburgh, Pennsylvania
Not to be outdone, the city of Cleveland has the Rockefeller Greenhouse, a hidden gem in the heart of the city, and the Cleveland Botanical Garden. The greenhouse was a part of John D. Rockefeller's estate and is now free to the public.