Tickets are free. However, there are a limited amount given out on the day of and you can not purchase in advanced. If you buy tickets on line (day of visit) there is an electronic fee of $1 per ticket, and you want to be on at 6 a.m because they do go FAST.
Free, but make sure the main exhibit tickets are still available
Free
Free to the public.
Zero but you need to get them to enter the main exhibit.
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