IDEAS THAT AREN'T JUST DUNGEON CRAWLs:
-- CAT AND MOUSE --
"Sydney, we believe that a rogue terrorist cell has come into information on the existence of a Rambaldi artifact hidden somewhere in the city. Your mission is to get into the area, dodge the terrorist cells, and get the Rambaldi artifact. If you're seen, the terrorist cell will activate their backup plan, which is to destroy the complex, so it is IMPERATIVE that you not be detected."
-- OUTBREAK, WITH ZOMBIES --
A special CDC team is deployed to the area to ensure that all traces of the plague are gone. This was made over the arguments of other departments, who would rather just blow the place up and cave it in. To make things even worse, this "plague" actually results in the dead rising, and the CDC team finds itself desperately trying to escape hordes of shuffling zombies while negotiators on the surface try to stop the army from caving in the whole place in the interests of national safety.
-- TECHNOBRIGADOON --
The heroes have odd dreams that compel them to go into the closed-off section. There, they discover that the area is older than it first appeared. In actuality, the area that was sealed off hundreds of years ago was an area that had only recently been unsealed after being sealed off previously as "haunted". A sort of technological Brigadoon, the area is cursed to be accessible to mortals for only a few months before being sealed up for centuries. The party must solve the mystery of what agent placed the curse and why, possibly rescuing an ancient immortal creature who has lain in the center of the old section, trapped, for millenia.
-- BABYLON SQUARED, SORTA --
"We thought they sealed it off for being a plague area, but these people didn't die from any plague. They died of old age! And those strange people in the old clothing speaking a language we couldn't understand -- those are the original inhabitants! This is some sort of time-warped nexus!"
-- YOUR BASIC AGENTS OF PSI ADVENTURE IN A NEW AREA --
"The old 'Ring around the Rosy' story, dancing to keep the plague away? A fanciful tale. In actuality, a cult of Illithids were attempting to summon some sort of dark and malevolant force into this world, using their power to make the poor victims dance in a summoning pattern -- like alien crop circles or the old faerie rings. They were stopped by early agents, but not without horrible cost. The Illithids used a powerful psionic artifact to steal the vital essence of life forms and force these dances -- that artifact caused the Black Plague. And that artifact is somewhere in this sealed-off area. And we know that the Illithids are gonna be looking for it."
I dunno. I could do more and better if I weren't just making all that up, but come on -- it's a neat idea. You can do more than JUST a dungeon crawl with it.
-Tacky