You can go online and donate $20 dollars a person and print your tickets
You don't need one. You do need an appointment because I think they're only open to the general public on Sunday. Go online and you can make appointment and buy a ticket. They are $20 (donation).
You don't need an invite! They're open to the public most Sundays with tours at 10, 11, and 12 and you just reserve your spot online with a donation (there is also a season pass option). On those days they have a small gift shop open and they have a snack booth with food available to feed certain animals and delicious human food. Occasionally there are special events, like some of the residents' birthdays, but those fill up quickly so should be booked more in advance. There are also private tour options available during the week, but those cost more and require more scheduling notice.
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