Martha great question. The best time to visit Seattle Center depends on what you plan on doing when you are on campus. If you want walk around the 74 acre campus and see the various artworks, gardens, International Fountain and Artists at Play playground, then anytime during the daytime will work. All those activities are open and free to the public. If you want to visit one of the over 30+ arts, cultural and educational organizations on campus I would recommend you visit their websites to confirm admission costs and hours of operations as each will vary. I hope this helps. For more information about Seattle Center please visit, http://seattlecenter.com/.
The best time is July and August you find not too hot and rainys days
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