Go to Istanbul.

It's massively photogenic. And a highly caffeinated city with crazy energy and a pulse like a hummingbird's.
When I went to Key West, I came to conclusions very similar to Graham's. There were stalls all over the place selling chocolate-dipped key lime pie on a stick, for crissakes. It was the worst kind of tourist trap (especially Duval Street), saved only by excellent diving and wandering way off the beaten path looking for photos. At one point, I went looking for urban decay shots, mainly because I was pissed about people coming to Detroit and taking them. So I spent about six hours shooting empty hotels and abandoned sewage pipes just to get even.

Not exactly mature, but considerably different from your average island shot.
Unique stuff's out there, even in the most familiar, picked-over spots. You just have to dig.