Shoulders must be covered. Best yo take a light blouse to put on over a vest top. You also must have knees covered so no shorts.
I'm sorry I can't give you the definitive answer. I just reviewed some pictures and noticed all the female workers wore long sleeves. I would suggest a light weight long sleeve shirt to wear. If you are going on a tour, the tour operator would definitely be the most qualified to answer that question. If you are not using a tour operator perhaps you can ask for guidance from your hotel staff. We used Buffalo Tours out of the Marriott Renaissance River View and were extremely happy with every tour we took.
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