This is the final level - you can only get here once you finish all of the other levels and return to J'Nanin. It's the shortest of all the levels - it just centers around you and one building in essence. It's also the most 'humanly interactive' and, depending on what you do, can be the most frustrating one. Well, besides the point-on-a-pixel aspect of the nature level :)

The Myst 3: Exile Walkthrough