As they often do, my thoughts have tuned to Minecraft. Specificlly, what it would take to make a Minecraft Adventure world. For those of you who've never used the dangerous "/gamemode 2" command, Adventure mode is a version of Minecraft where your ability to gather blocks and otherwise manipulate your environment is severely limited, at least in comparison to other Minecraft modes where your only real limits to block manipulation are knowledge and time.
Adventure mode, as the name suggests, is a mode based more around conventional video game interaction rather than the self-motivated, directionless motif of Minecraft. Unlike the remainder of Minecraft, it requires a conscious architect. So what kind of challenges can you pose with a Minecraft Adventure World?