It's kind of a time travel thing -- the present is this giant barren wasteland with one little bastion of civilization that has just enough power to send you back in time to a region full of Fields.
Your goal is to collect Artifacts deep within mazes -- each one will add enough power to form a Time Bridge to another region.
The Ancient City region has you go even further back in the past, while the Meteor region has you go in the future (from the present's perspective, even). Both of these tie heavily into the plot and there's a bunch of time manipulation going on in the course of these two region quests.
