I've yet to send any clientele on this secret experience, but it was brought to my attention by a Royal development manager during a ship inspection I enjoyed on the Allure of the Seas some time ago...
The Oasis Class ships from Royal Caribbean have a planted garden area on the surface of their central-most decks, their Central Park.
The feature includes a number of live plants, shrubs, and even real trees!
The thing that very few people are asking themselves is, how do they keep them alive at sea!?!
There's apparently a secret tour operating once per sailing on 7-night or longer itineraries, in which a few people can enjoy a little horticultural tour to see just how they do keep the gardens looking so beautiful on deck and throughout the year!