Business casual. The comment above suggests Semi-formal, but I completely disagree, because it insinuates jacket and tie, and that would be overkill here. In fact, there were tourists dressed casually, and they absolutely seemed underdressed as well. Business casual is the right balance here.
Semi formal, business casual. No jerseys or gym clothes.
Semi formal
I recommend semi-formal, kind of like the outfit you'd wear to a night club
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