Visitors center, very nice and friendly. $30 for the week
Pass can be bought online too. At the visiter center they would give you the idea about where to go first and parking positions of different locations. They also give the pass to hang on rear view mirror. Visitor center has around 50 stairs, in case you are not fond of them, better buy online :)
Or just go to the visitors center
Online or at the visitors center
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