Tickets can be purchased at machines outside the entrance or at a ticket window. For pricing: https://www.911memorial.org/visit-museum-1
We bought tickets online. When we got there, the line was sooooo long for those buying on site. We were directed to another line that had only two people in front of us. We were extremely thankful we pre-purchased tickets.
When I was there, there was a long line to buy tickets. So maybe it's best to buy before coming.
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