Tickets are free. Sometimes it is possible to walk in-- don't take any chances. I would get the tickets as advised; you will be better off. Timing is everything.
We went yesterday, Tuesday Feb. 19, 2020 and we were able to talk right in. But I've heard getting the tickets in advance is definitely advisable and well with the effort. It's an absolutely incredible experience that you won't forget.
Free, but they must be claimed in advance on the website nmaahc.si.edu
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