I've looked for other movies like my idea, but....

[fyifoff.livejournal.com]

The simple plot info of my story is: 

Two people find out that they live on top of a lost city. The military and raiders are closing in as these two people enter the underground city, they get seperated, have to say alive and avoid the military and raiders.  Middle and then the end, detail don't really matter...

Here is my problem:

I know there is a 'lost world' genre, but my lost city is 98% lifeless. 

What movies/novel do you think of that would be great "research" for me

thanks