Recomended to purchase in advance. But you can always pirchase at entrance
You can purchase it there.
They do suggest you buy the tickets in advance online. There is no guarantee that tickets will be available if you buy in person at the ticket window.
I believe they are asking you to go to the website and reserve your tickets/ time slot in order to maintain a smaller capacity. If you buy online ahead of time, you don't even have to stand in line at the box office if you request mobile tickets so you can just scan and go in. I went yesterday and it's so easy that way!
I would purchase in advance.
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