One thing that I've noticed while playing Traveller that I had not noticed much previously (keep in mind that I was attracted by the erroneous "storytelling" paradigm when I started to think seriously about adventure games, it being the dominant paradigm of the time) is the interrelation of various minigames (or perhaps "subsystems") as parts of the flow of play. As I prepare for the Terra Ultima game, I naturally am thinking about the sorts of minigames to make available.
The obvious ones are built into the main rules: combat, exploration and encounter in the dungeon and wilderness, NPC reactions, the "endgame", and so on. It seems like there are others, though, that should be available to the players. I am thinking here of ones that are obviously inspired by Traveller, such as a merchant minigame of speculative trade. I suppose that I'd do that in a manner based on Traveller's speculative trade system. Other examples might include astral exploration (different not only in appearance, but in basic format from standard wilderness or dungeon exploration).
What minigames (or subsystems, if you prefer) do you think should be available to the players at various points in the game?