Leak by rear driver side

Oh, ye Prius gods,

So I just got home & noticed this in my garage. It must have been there before I left, but didn't notice it this morning. Any thoughts on what it could be???

Help!

 

Here are more pics. I saw it dripping from this part. It's in the middle of the rear of the car.

 

So...crisis averted. We found a giant puddle of coffee where the spare tire is (but nothing above it). We figured out that I had my 12v battery changed about a year ago, so that would have been all opened up. One of the guys must have spilled coffee in the wheel well. And I live in a very warm climate, but it's been down in the 30's at night for the past couple of days, so the plastic stoppers that are there must have shrunk and the coffee started leaking out! I feel very sherlock holmes and only partially idiot. In any case, I'll make sure and thank pep boys for their diligence in cleaning up their mess before they give their customers their cars back. UGH. But thank you for the reply!