The Fortress Eternal: Basic Concept

In all honesty, I probably ought to get the central idea - or at least the initial draft of it - down on paper. I work around it a lot; this is much the same as what I used to do in art class, when I'd do very detailed drawings of people, paying attention to everything except their faces. The odd faceless portraits I ended up doing creeped the art teachers out, and I never had time to add faces at the end of the class.
What I'm doing here - sporadically, I'll admit, but still technically doing - is similar. I've had a fair few ideas for roleplaying games over the years, but nothing ever really gets done with them. So, I thought I would get the actual core notion behind The Fortress Eternal written down so I can see it, modify it, and get some ideas behind what it actually means. So, here it is:

The players are explorers lost, or trapped, within a city that spans eternity and where death has no meaning. They seek to unravel its mysteries and perhaps escape - though to when, they cannot be sure.

So there it is: The Fortress Eternal. The City is Forever.