What and where?

Since Dissenter got the last one so quickly, I thought I'd indulge in another bit of shutter-buggery.
What is this and where is it located?
Again, it's not terribly far from the Quad Cities.

I've also posted a few pictures from a couple geocaching adventures, including a couple which feature yours truly. I didn't want to bore those not interested here by taking up all the space, but you can see the (crude) page here.