If you go to
Janet2K's photo site, she has pictures taken with her and her daughter dining out on the 3rd floor terrace. I'm pretty sure the way the building is setup, you wouldn't have a clear view of the fireworks.
I'm guessing that when they say the 5th floor balcony, they mean the hallway area along the balcony. I've sat up here during the day, but, I'm sorry, I can't really recall the view. You would be up much higher and maybe have better clearance over the roof to see the fireworks. The lounge is on the 4th floor, so other than foot traffic from guests having a room on the 5th floor, you would have privacy. Janet can probably answer the question about the 3rd floor terrace and whether other guests came out there. I can say from past experience, that rarely did we see anyone using the terrace.
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