Myst Online: Uru had Ahnonay.
Essentially, it was a "secluded island" with other islands off in the distance. With a bit of puzzle solving, it suddenly transformed into a decrepit rock in a sea of fog. A bit more exploration, and it tranformed into a rock in space, then back into a secluded island.
Then, by manipulating the linking system a bit, you could turn off the water currents and swim out to the distant islands... where they turn out to be painted on giant flats.
With more exploration and mucking behind the scenes, you could transform the island into a giant incomplete statue hanging in a big dome. With a bit of manipulation and help from a friend, you could eventually end up UNDER the island version of the area, in a sleeping area, just watching the waterfall completely surrounding you. It was breathtaking.
Best level design ever.
From the same game, the open area at the top of the first tower in Gahreesen was basically a quick blast of pure scenery porn.