The description of the penthouse is correct. It is twice the size of the royal suite and the layout is very different plus there is a hot tub on the balcony.. There is no Butler's pantry in the Royal Suite.
Here is the description and diagram of the Royal Suite:
I have been in (but never stayed $$$ ) in the Century and Mercury Penthouse and they are VERY nice and almost identical. I have also stayed in a Royal Suite, on Mercury and IMO I would go for the Royal Suite for a couple. It is almost identical to the one on Century and for two people you will receive the same luxury for greater than half the price.
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