Hello.
I've always been fascinated by the idea of having whole cities retaken by wilderness.

There was a TV show a couple months back that dealt with the idea of what would happen if man ceased to exist. Our modern buildings would last maybe 100 years or so.
I like the idea of pockets of technology and modern architecture existing in jungles and mounds of vegetation. The mutations and the way creatures would adapt to the new world would be fun to extrapolate on.

Good luck with your project.

-D