Erik, of American in Spain, finally guessed that it was a madroño fruit. In English, the plant this fruit grows on is called a strawberry tree, although the fruits are not strawberries, and while they are edible, they are nowhere near as nice as real strawberries. The bush itself isn't all that special, but when it's full of red berries, it is pretty spectacular.
|This is the fruit as seen from the bottom, and the photo I used for the contest.|
The madroño, or Arbustus unedo, is fairly common here in Spain, and is found on Madrid's coat of arms, which depicts a bear eating the fruit off the tree.
If you visit Madrid, you'll find this symbol in many places, including this statue, which is located in Puerta del Sol.
So, congrats to Erik, for figuring this one out. I guess it was kind of a tough one. And thanks to everyone else for playing along. I'll be back on Friday, this time with something easier, I promise.