Trees, ground, water as rivers and lakes, with animation. Animals or objects, like boats, with animation. Logic to generate new terrain as you explore to a boundary, all saved to disk, and logic to where and how animals move, appear and disappear, all saved to disk.
The idea was to complete this, then use it to make a treasure hunting game, a pirate treasure/sailing game, or just to see how nice of a self-generating world I could create. It's been slow going! No game yet, just world creation.