The tour is free, but it is recommended that you schedule the tour ahead of time. There is very small chance that you can walk in unless you are very lucky that someone scheduling the tour does not show up.
The tours have specific starting times and require you to be present a certain time before the tour begins.
The tours are free but require a ticket. There is a limited number of tickets, but if it is not busy you can get a ticket just before a tour starts.
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