I'm quite new to the guest happiness thing [I ususally ignore guests completely], but may I suggest adding a lot of flowers, in combination with statues and fountains. Be sure to make it look nice, not just random. Benches also add a nice touch. I did all of that and in my guest thoughts they said it 'looked lovely.' If you want screenshots of what I mean, there's some
here [see Rest Area, Pyramid, Pyramid Change, Merry-go-Round, and Landscaping for specifics].
Hope that helps and good luck. :
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