In summer Immortal Valley is filled with the pleasant sound of running water, with streams running down and out of a deep canyon. In winter, the streams, pools, and waterfalls freeze over.
The first half of this hike was very cold - we walked up the canyon, passing frozen pools and waterfalls. The canyon is quite deep, so no sun reaches the path along the bottom. We measured the temperature as -10°C, and we could really feel the chill when not walking.
The second half of the hike was much warmer. We climbed out of the canyon and up on to a ridge, finally seeing some sun. We followed a trail along the ridge, passing rocky outcrops on the way back down to the valley trail. As we walked down we had excellent views of the Miyun Reservoir, the surrounding mountains, and some of the Great Wall in the area.