This is a photo of Carandiru II. At some point (and the park's signs don't give much information), there was a plan to build more cells for the Carandiru prison complex. You can see the concrete supports are already up here. But as the construction languished, the plants and trees took over. Now the park has built a walkway through so you can see a bit of the structure of cells. To me it was an interesting reminder of how prisoners give up the lightness of day and the beauty of nature.
In the very background of this shot are two young men battling with fake axes and other medieval equipment. One was wearing a knight's tunic. Practicing for a play? Not sure, but it was a perfect place for it.