A collared shirt and a tie are recommended. It is a pretty special place.
When I went I felt overdressed wearing a tie and jacket. Someone walked in with shorts. But overall I would suggest a collared shirt and pants.
It is a special place that warrants special clothing. I would say at least a collared shirt for men with a sport coat on top. A necktie would be most appropriate.
I saw people in the dining room in various states of dress, but most men were in suits or at least sport coats. It does warrant dressing well, its a beautiful venue with fine dining and impeccable service.
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