Reservations are not required but are highly recommended. The tours start at specific times and sometimes they fill up. So the walks are taking a risk and it's a tour with availability that will start soon.
For a larger group I would suggest calling ahead and reserving. For just a few people you should be able to go as walk ins. This is however a popular local attraction, so I would suggest calling or going online and reserving a time to guarantee you get on the course.
We called and got a time. They can control the groups that way. I am sure they take walk ins
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