Frozen River

Should the newly-released tributes at the Cornucopia glance to their east, they may not realize what they are looking at. They can hardly be blamed; at first glance, this land looks exactly the same as that at the Cornucopia's base, snowy with occasional traces of ice. Further inspection, however, will reveal that this long stretch of "land" is actually mostly ice, with only a veneer of snow. As one moves away from the Cornucopia, this becomes more apparent; snow-bearing clouds rarely hover over the ends, so tributes walking there can tell that they are actually standing on what once must have been a moving, liquid river. As far as anyone can tell from looking, it's currently frozen all the way through. There may be water underneath, and if so breaking through could be valuable, but it would take a long, long time to find out...