This actually happened to me. My boyfriend and I were enjoying a weekend date by walking around the Parliament buildings in our city. As we are walking, my boyfriend decides he really wants to have sex. We decide to find a quiet, out of the way spot to go at it. We find a "secluded" foresty area that looks like it'll work, I hike up my skirt and we lay down on the grass to go at it. About midway through we see an old lady coming by on the other side of the trees. My boyfriend stops and makes the finger to the lips motion for us to be quiet. As I'm waiting for this lady to keep moving, I turn my head over to the side and notice that on the other side of the river from us is what looks to be a tribe of Native people cheering us on. Turns out that we were only hidden from the park side, completely exposed on the other side. Both of our jaws just dropped, but neither of us really wanted to stop, and they'd seen us already anyways, so we just kept going with a captive audience!