Look on their websites for times and tickets. You don't have to book in advance but I would suggest that you do so you can get the time you want since it's a holiday weekend there might be a lot of people.
Book ahead on line. It's the only way to guarantee you'll get the tour you are interested in going on.
Tours run regularly, about every 15 minutes or so based on the amount of guides available. Group size is limited. Book early to get a spot.
Yes you have to book in advance. I would suggest calling and getting a reservation or doing it on the website. Don't expect to get a great tour if you show up that day. They are worth every minute.
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