Tianchi, or Heaven Lake, is a lake in a caldera atop the Changbai mountain range which straddles China and North Korea. In winter, the lake is completely frozen, and seeing it from the peak of ChangBaiShan will certainly take your breath away, in more ways than one. At 2600+m, -28°C, and howling wind speeds, I needed the lake's beauty to distract me from the harsh conditions. It was indeed quite challenging for photography!!
However, access to the peak seems to be quite controlled. There are specially designated jeeps that bring you up to the peak's visitor station. Perhaps this is a good thing, since you wouldn't want to wander into North Korea territory... From the visitors station, its just a short trek to the lake viewpoint. Although it was extremely cold, I am glad I made the trip!!